Which is the correct name of this compound? *
N₂03
2 pts

1.22 m below the surface of a swimming pool's bottom lies a little light fixture. The circumference of this circle is 2.27 m.

One of the fundamental and common symbols is light. It is the holy and the spiritual; it is wisdom and insight. Light is the wellspring of kindness and the true truth; according to Buddhist belief, it also follows transcendence into Nirvana.

The critical angle is found by imagining the refracted ray just grazing the surface (θ₂ = 90°). The index of refraction of water is n₁ = 1.333, and n₂ =1.00

for air, so n₁ sin∅​c = n₂ sin90° gives ∅c =sin⁻¹ (1/1.333)= sin⁻¹ (0.750)=48.6°

The radius then satisfies

tan∅c = r/1.00m

​So the diameter is

d=2[(1.00m)tan∅c]

d=(2.00m)tan48.6° = 2.27m

To know more about Light visit:

https://brainly.com/question/15200315

#SPJ4

​

That seems relatively fast to me. Wave speed is typically between 160 to 320 km/h, so the 4.5 hours it would take for these waves to travel from the buoy to the coastline is in line with the expected wave speed.

What is Wave?
A wave is a spreading dynamic disturbance (transition from equilibrium) with one or even more quantities in physics, mathematics, as well as related fields. When a wave is periodic, its constituent parts repeatedly oscillate around an equilibrium (resting) valuation at a given frequency. A travelling wave is defined as one in which the a whole waveform moves inside one direction; in contrast, a standing wave is defined as a pair of superimposed promotes the flow moving in the opposite directions. In a standing wave, the vibration's amplitude nulls out at certain locations where the wave's amplitude appears smaller and even zero. Wave equations, which are standing wave fields of two opposing waves, or one-way wave equations, which describe the propagation of a single wave in a specific direction, are frequently used to describe waves.

To learn more about Wave
https://brainly.com/question/28447252
#SPJ4

A one corresponds to the greatest magnitude of acceleration of the particle.

What is acceleration?

Any procedure where the velocity varies is referred to as acceleration. There are only two ways to accelerate: changing your speed or changing your direction, or changing both. This is because velocity is both a speed and a direction.

The graph given is of Kinetic energy rs position. Kinetic energy [tex]$K \cdot[/tex] [tex]E=\frac{1}{2} m v^2$[/tex]. Since mass ' m ' is Constant we can write K.E [tex]$\propto v^2$[/tex]

So when kinetic energy is maximum, speed is maximum. when kinetic energy is changing/increasing at maximum rate implies speed is also increasing at maximum rate implies acceleration is maximum. So when acceleration of the particle is zero, slope is zero. ie rate of change of kinetic energy is zero. So the answers ave:

1) Acceleration zero: B, D, F & H.

2) A, E, G; out of these 3 points, at[tex]$A^{\prime}$[/tex] the slope is maximum.

[tex]$\Rightarrow$[/tex]At 'A', acceleration is maximum.

3) Maximum[tex]$K \cdot E \Rightarrow$[/tex] highest point : 'B' Corresponds to highest K.E.

4) Lowest speed corresponds to lowest kinetic energy. [tex]$\Rightarrow$[/tex] ' D '

To learn more about  kinetic energy visit:https://brainly.com/question/15764612

#SPJ4

The speed of visible light waves when travelling through a vacuum is about 3 X 10⁸ m/s.

What is electromagnetic waves?

In terms of science, electromagnetic radiation is made up of electromagnetic field waves that travel over space while carrying radiant electromagnetic energy. It consists of X-rays, gamma rays, microwaves, infrared, light, and radio waves. These waves are all a component of the electromagnetic spectrum.

The speed of electromagnetic waves, which includes visible light, radio light and x-rays is 3 X 10⁸ m/s. This is same as that of the speed of visible light in the presence of air.

The speed of light is depicted using the letter 'c', and it a universal constant value. It is a physical constant and important in many areas of physics.

The speed of light in water is 2.25 X 10⁸ m/s and that in glass is 2 X 10⁸ m/s. The speed varies with respect to the medium.

To know more about Speed of light:

brainly.com/question/1675384

#SPJ4

The magnitude of the acceleration of the block after the system is released from rest is: ablock = 3.27

What is magnitude?

Just as the magnitude of an earthquake indicates its strength, the magnitude of a mathematical term indicates its magnitude. In mathematics, this means how far a mathematical term is from zero.

For numbers like 1, 2, 3, the magnitude is simply the number itself. If the number is negative, the magnitude is the absolute value of the number. For example, the magnitude of 10 is 10. The magnitude of -10 is the absolute value of -10, which is 10. In both cases, the magnitude is the distance from zero of the mathematical term. Both 10 and -10 are 10 distances from zero.

Thus, The magnitude of the acceleration of the block after the system is released from rest is: ablock = 3.27

To know more about acceleration, check out:

https://brainly.com/question/460763

#SPJ4

54.2 MJ of energy could be used as mechanical energy from heat engine  operating between 317 c and -3 c and if the engine extracted 100 mj of energy from fuel.

What is mechanical energy ?

Mechanical energy, also known as kinetic energy or potential energy, is the energy that an object possesses when it is in motion or the energy that an object stores due to its location.

According to the given information:

T(high) = -3 °C

T (low) = 317 °C

Fuel extracted = 100 MJ

First we need to convert temperature into kelvin

T(high) = 270 K

T(low) = 590 K

Efficiency = 1 -  [tex]\frac{T(high)}{T(low)}[/tex]

Efficiency = 1 - [tex]\frac{270}{590}[/tex]

Efficiency = 1 - 0.458

Efficiency = 0.542

Hence maximum useful work done = 0.542 x 100 MJ

Maximum work done or the amount of energy used as mechanical energy = 54.2 MJ

Hence the maximum amount of useful work extracted from the heat engine is 54.2 MJ

To learn more about energy click here:

https://brainly.com/question/5144470

#SPJ4







The inductive reactance is 4.00 times as large as the capacitive reactance is 10.1 Hz or 6.26 radians/sec.

What is inductive reactance?
The resistance provided by the inductor inside an AC circuit to a flow of ac current is known as inductive reactance. Its measurement unit is the ohm (Ω), and its symbol is (XL). For lower frequencies, inductive reactance is typically low, and for higher frequencies, it is high. However, it is insignificant for constant DC current.

The angular frequency (ω) at which the inductive reactance (XL) is 4.00 times as large as the capacitive reactance (XC) is given by the following equation:
XL = 4.00 XC
ωL= 4.00 ωC

where ωL is the angular frequency for the inductor and ωC is the angular frequency for the capacitor.
The angular frequency for the capacitor is given by the following equation:

ωC = 1/(2πRC)
where R is the resistance in ohms and C is the capacitance in farads.
Therefore, substituting the given values of R = 85.0 ohms and C = 14.0 μF, we have:
ωC = 1/(2π*85.0*14.0*10-6) = 2.47 radians/sec
The angular frequency for the inductor is given by the following equation:
ωL = 2πFL

where F is the frequency of the AC source in hertz and L is the inductance in henries.
Therefore, substituting the given values of F = variable and L = 1.50 mH, we have:
ωL = 2π*variable*1.50*10-3 = 6.28*variable radians/sec
Combining the two equations, we have:
6.28*variable = 4.00*2.47
Solving for the variable, we get:
variable = 6.28*4.00/2.47 = 10.1 Hz
Therefore, the angular frequency at which the inductive reactance is 4.00 times as large as the capacitive reactance is 10.1 Hz or 6.26 radians/sec.

To learn more about inductive reactance
https://brainly.com/question/4425414
#SPJ4

The wire bends more than it did before when the switch is closed and the direction of the current is reversed in the wire.

A stream of charged particles such as electrons or ions moving through a conductor for electricity or into empty space is known as an electric current. The net rate of passage of electric charge through a surface or into a control volume is used to measure it. Charge carriers are the moving particles, which depending on the conductor could be any number of different types of particles. Often, electrons flowing over a wire serve as the charge carriers in electric circuits. They may be holes or electrons in semiconductors. Ions are the charge carriers in an electrolyte, while electrons and ions make up plasma, an ionized gas.

Learn more about current here:

https://brainly.com/question/12249228

#SPJ4

If a student uses two strong forces to lift a 1 kg book using two cables, the tension in the cable will be 562.1 N if the cables are at a 1 degree angle with the horizontal.

Tension is a pulling force that operates in one dimension along the cables' axes in the opposite direction from the direction of the applied force. The combined weight of the elevator box and the person riding inside it, in the case of an elevator, provides the pulling force in the cables is called as Tension.

There are four basic interactions that encompass all known forces in the cosmos. The interactions between subatomic particles are caused by the strong and weak forces, which only operate over very small distances.

F1 sin(tetha)+F2 sin(tetha) = F3

F1 cos(tetha) =  F2cos(tetha)

2F1 sin (tetha) = 2*9.81

F1 sin (1) = 9.81

F1 = 9.81/sin(1)

=562.1N

Learn more about tension here

https://brainly.com/question/28965515

#SPJ4

The wavelength of the light is 6.21 × 10⁻⁷ m.

Single-slit diffraction has an equation

d sin θ = m λ

where

For a small angle, sin θ = tan θ.

θ is the angle where the opposite of the angle is the width apart near the center of the pattern (x) and the adjacent is the distance between the screen from the slits (L). So [tex]tan \: \theta = \frac{x}{L}[/tex]

d sin θ = m λ

d tan θ = m λ

[tex]d \: \frac{x}{L} \:=\: 1 \times \lambda[/tex]

[tex]\lambda \:=\: 4.4 \times 10^{- 5} \times \frac{8.9 \times 10^{- 2}}{6.3}[/tex]

λ = 4.4 × 10⁻⁵ × 1.41 × 10⁻²

λ = 6.21 × 10⁻⁷ m

Learn more about single-slit diffraction here: https://brainly.com/question/13151128

#SPJ4

Answer: 80 mph

Explanation:

The original mass of the sample was 14.79 grams.

We know that rate of reaction of first order reactions is given by: [tex]kt = 2.303* log(R'/R)[/tex]

where k = rate of reaction = 0.0198

           t = time = 98.3 days

           R = final mass = 2.14 grams

Putting these values in above equation we get R' = 14.79 grams.

i.e. The original mass of the sample was 14.79 grams.

To know more about radioactivity visit:

https://brainly.com/question/20039004

#SPJ4

The current in the circuit with the coil is greater than the current in the circuit with the uncoiled wire

Electric current is the flow of electric charge in a circuit.

Since a long wire of finite resistance is connected to an ac generator, in this circuit, we know that the length of wire has a resistance and will draw a current from the generator.

Now, the wire is then wound into a coil of many loops and reconnected to the generator, the wire now has an inductance. In this circuit, the inductance of the wire causes it to draw extra current apart from that drawn by the resistance of the wire.

So, since it draws extra current, thus, the current in the circuit increases when the long finite wire is wound into a coil of many loops.

So, the current with the coil is greater than the current in the circuit with the uncoiled wire

Learn more about current in coil of wire here:

https://brainly.com/question/28556224

#SPJ1

The energy absorbed by Hydrogen atom to transit an electron from n = 3 to n = 6 is 1.815x10-19 Joules

Energy Level: According to the Bohr atomic model, energy levels—also known as electron shells—are thought of as the orbits that electrons in an atom's nucleus take. Electrons must always be in one of the energy levels and never in the space between them since the energy levels represent defined distances.

According to the given information

Change in energy = [tex]-13.6eV \frac{1}{n_{f} ^{2} }-\frac{1}{n_{i} ^{2} }[/tex]

                              = -13.6 × 1.6 × [tex]10^{-19}[/tex] ( [tex]\frac{1}{6^{2} }[/tex] - [tex]\frac{1}{3^{2} }[/tex] )

                              = 21.76 × [tex]10^{-19}[/tex] × 0.084

                              = 1.815 × [tex]10^{-19}[/tex] J

Change in Energy level = 1.815 × [tex]10^{-19}[/tex] J

The energy absorbed by Hydrogen atom to transit an electron from n = 3 to n = 6 is 1.815x10-19 Joules

To know more about Energy level

https://brainly.com/question/17396431

#SPJ4

Answer: B. Muscular fitness training increases muscle mass, which increases your metabolism

The box accelerates down the incline at 2.4m/s^2.

A mass m particle will slide down a smooth inclined plane if it is released onto it with a friction force F=0. We resolve in the direction of motion to determine the particle's acceleration as it slides. F = ma, mg cos(90) = ma, gg cos(90) = a, gg sin() = a.

By using zigmaFx = max, we will determine the acceleration.

However, we must first determine the friction force Ff.

Because cos 30 degree = 0.866 and Fy = ma y = 0 result in FN - 0.87mg = 0, we may calculate FN as (0.87)(20Kg)(9.81 m/s2) = 171N.

From Ff = mue FN = 0.30)(171 N)= 51N, we can now calculate Ff.

We get Ff - 0.50mg = ma x 51N - (0.50)(20)(9.81)N = (20kg)(ax) from the expression zigmaFx = max, where ax = -2.35 m/s2.

At 2.4 m/s2, the box quickens its descent of the hill.

To learn more about acceleration refer to:

https://brainly.com/question/460763

#SPJ1

The amount of work that the engine of the spacecraft must do to move above the circular orbit is 1.48 x 10⁻¹⁷ mM (Joules).

The established fact that the gravitational attraction between two objects varies also on square of their distance leads to the geometry of planetary orbits. The attractive product of two items decreases to a fourth of its initial amount when the distance between them is doubled.

W = Fd

where;

F is the spacecraft's gravitational field,

d is the displacement of the spacecraft.

The spacecraft's gravitational pull is specified as;

F = GmM/R²

where;

m is the planet's mass (for the circular orbit)

M is the spacecraft's mass.

R is the spacecraft's displacement.

The tasks that the spacecraft must complete are as follows:

W = FR

W = GmM/R² x R

W = GmM/R

W = (6.67 x 10⁻¹¹ x mM) / (4500000)

W = 1.48 x 10⁻¹⁷ mM (Joules)

To know more about Circular orbit visit:

https://brainly.com/question/14832572

#SPJ4

a) Displacement current density  for the capacitor is  113.4 A/m²

b) Rate of change of the electric field is   1.48157826 V/m.s

c) Magnetic field between plates at r of 1.93 cm  is  5.563×10⁻6 Tesla

d) Magnetic field between plates at r of 1.10 cm is  7.833 x 10-7 Tesla

Since we are given the radius of a parallel-plate capacitor which is 4.00 cm( 0.04 m) and the Conduction current = Ic =  0.570 A .we know  the  formula for the Displacement current density is

JD = Id/A, where  Id is the conduction current and A is the area of the capacitor, and A= πr² = π(0.04)²= 0.005024 m². As we know  conduction current has equal displacement between the capacitor plates so  Id = Ic

JD = 0.570/0.005024  = 113.4 A/m²

For the second case, we know the  rate of change of the electric field is:

dE/dt = JD/ε₀ , where JD is the displacement current density and ε₀ is the permittivity of free space (  8.854×10⁻¹² C²/N.m²)

so, dE/dt = 113.4/8.854×10⁻¹² =1.48157826 V/m.s

for the third case, the formula for The induced magnetic field between the plates  will be :

B = (μ₀/2)*JD*r, μ₀ is the permeability of free space(4π×10⁻⁷ T.m/A)and r is the distance from the axis.

B = (4π×10⁻⁷/2)*113.4 *0.01953

B = 5.563× 10⁻⁶ Tesla ,and for the last case, for the radius of 1.10  cm (0.011 m)

B = (μ₀/2)*JD*r

B = (4π×10⁻⁷/2)*113.4 *0.011

B = 7.833 x 10⁻⁷ Tesla

To know more about capacitors refer to the link brainly.com/question/17176550

#SPJ4

The reading of the scale due to the two masses, massless string and the frictionless pullies is 0.

When the strings have frictionless pullies, they perform a rotary motion with the pulleys.

Net force of the masses

The two masses are connected by massless spring.

Since the masses are at rest, the sum of all the forces acting on the scale will be zero.

Fnet = o

T + M1g - M2g = 0

M1 and M2 are the masses at rest respectively.

T = M2g - M1g

Reading on the scale

Since the two given masses have same mass then their product with 'g' is  and their difference is zero.

The reading of the scale is equal to the tension in the pulley connecting the two masses.

The tension on the pulley is calculated as follows;

T = Mg - Mg

T = 0

Thus, the reading of the scale due to the given masses is 0.

To know more about frictionless pullies,

https://brainly.com/question/14989341

#SPJ4

The chain supporting the basket is at a 45° angle to the vertical and horizontal component is 1244.6N.

When an object's speed stays the same and neither increases nor decreases, we say it is moving at a constant speed.

Mass of the person is 82kg and mass of the basket is 45 kg.

New total mass, M = 82+45 = 127kg.

Here, Fe is centrifugal force

v is velocity of the person

r is radius of the circle,

r = 7.1m

Now, Tsin 45° = Mg [ here Mg is weight of person and basket]

T = Mg/sin 45° = Mg√2

Now, vertical component of the tension,

Fy = Tsin 45° = Mg = (127×9.8)kg-m/s²

Fy = 1244.6N

Now, horizontal component,

Fx = Tcos 45°

Fx = Mg/Tan 45°

Fx = Mg/1

Fx = 1244.6N

To know more about speed visit:

https://brainly.com/question/28224010

#SPJ1

The force of gravity acting on the column of water is 1,02,900 N.

Given that, height of the liquid column is 7

Area = 1.5 m²

We know that, volume of water = 1.5* 7 = 10.5 m³

10.5 m³ when converted into litres can be written as 10,500 litres

Water mass = 10,500 litres * (1kg/litre) = 10,500 kg

Force of gravity on water is nothing but weight of the water

⇒ 10,500* 9.8 = 1,02,900 N

Pressure on the bottom of the tank = 1,02,900/1.5 = 68,600 N/m² = 68,600 pascal

Thus, the force of gravity acting on the column of water is calculated to be 1,02,900 N.

To know more about force of gravity:

https://brainly.com/question/9032621

#SPJ4

Early Mars (extra than three billion years in the past) strong greenhouse effect. Substantial volcanism and outgassing. Strong magnetosphere.

*Some craters held lakes of water.

*Core convection.

Mars Today:

*Surface pressure too low for stable liquid water.

*Solar wind strips atmospheric gas.

*Very weak greenhouse effect.

A gas is a substance that has no constant size or form. Whilst inside a closed container, gasoline will amplify to fill the field. An instance of gas is the air you breathe. The gas interior of your digestive tract is fabricated from the air and different gases.

Traits of Gases :

* Gases have neither definite shape nor particular volume.

* Gases are fluid and go with the flow effortlessly.

* Gases have low density, except compressed.

* Gases diffuse (mix and unfold out) and effuse (tour thru small holes).

Learn more about Gases here:-https://brainly.com/question/20349818

#SPJ4

Diffuse dome lighting method has a light source placed inside the surface of a partially reflective dome, with the camera focused on the object through a hole in the middle.

What is Diffuse dome lighting?

Machine vision dome lights, commonly referred to as "cloudy-day illumination," produce diffuse lighting. Reflected light offers gentle, shadow-free lighting that is non-directional and non-directional. At close working distances, this effect is ideal for scrutinizing highly specular, curving objects.

The CCD stands for a Charge Coupled Device, which is a semiconductor element that converts images into digital signals.

Cameras are used by machine vision to collect visual data from the surroundings. It then prepares the data for usage in various applications by processing the photos using a mix of hardware and software. Specialized optics are frequently used in machine vision technologies to capture pictures.

To learn more about Diffuse dome lighting visit:https://brainly.com/question/14812320

#SPJ4

A uniform solid 5.25-kg cylinder is released from rest and rolls without slipping down an inclined plane inclined at 18° to the horizontal. Its speed while rolling down is 3.0 m/s.

The mass of the solid cylinder, [tex]m=5.25 kg[/tex]

The inclination of the plane, θ=[tex]18^{0}[/tex]

The speed of a solid cylinder rolling down an inclined surface is calculated using the following formula:

The kinetic energy of the cylinder

[tex]K=3/5 mgh[/tex]

[tex]1/2mv^{2} =3/5 mgh[/tex]

[tex]v=\sqrt{6gh/5}[/tex]

Substituting for the values h as [tex]h=mgcos[/tex]θ

we get the speed as

[tex]v=3.0 m/s[/tex]

To know more about speed of a solid cylinder rolling down here

https://brainly.com/question/13975091

#SPJ4

A toggle clamp is a tool that you use to firmly secure components or pieces in place, frequently but not always as part of a production process.

A toggle clamp is a device that you employ, often but not exclusively as part of a production process, to firmly place components or parts in place. A toggle clamp's main characteristics are its rapid action and ability to be easily turned on and off by an operator.

Toggle clamps also lock in place firmly. Because of this, toggle clamps are frequently employed in production lines where components need to be held firmly and quickly removed during routine manufacturing procedures.

Toggle clamps come in six primary categories: vertical toggle clamps, horizontal toggle clamps, plunger toggle clamps (also known as push action toggle clamps), hook action toggle clamps, plier action toggle clamps, and cam action toggle clamps.

learn more about toggle clamp here:

https://brainly.com/question/29676776

#SPJ1

The ball was moving at 11.1 m/s in the horizontal direction just before it hit the ground.

What is horizontal direction?
Horizontal direction is a term used to describe a direction parallel to the horizon. It is an important concept in navigation and surveying, since it helps to determine a person's geographic location. Horizontal direction is usually expressed as an angle, measured clockwise from the direction of true north. It is important to remember that the angle for horizontal direction increases as the person turns clockwise from true north. For example, if a person were facing north, their horizontal direction would be 0°. If they were facing northeast, their horizontal direction would be 45°. In addition to its use in navigation, horizontal direction is also used in architecture and engineering. For example, when designing a building, architects use horizontal direction to determine which way the building should face in order to maximize the amount of natural light that enters the building.

We can use the equation vf^2=vi^2 + 2ad, where vf is the final velocity, vi is the initial velocity, a is the acceleration due to gravity (9.8 m/s^2) and d is the displacement.
In this case, vf = 0 m/s (since the ball has stopped moving at the end of its fall), vi = unknown, a = 9.8 m/s^2, and d = 3.32 m.
We can rearrange this equation to solve for vi: vi = sqrt(vf^2 - 2ad)
vi = sqrt(0^2 - 2(9.8)(9.47)) = -11.1 m/s
Since the velocity is negative, it is moving in the opposite direction of the displacement. Therefore, the ball was moving at 11.1 m/s in the horizontal direction just before it hit the ground.

To learn more about horizontal direction
https://brainly.com/question/25854506
#SPJ4

The sun rotates in the counterclockwise direction when viewed from above the North Pole of the Sun.

The Sun rotates on its axis approximately once in 27 days. This rotation was first discovered by observing the motion of the Sun. The Sun's axis of rotation is tilted by about 7.25 degrees from the axis of Earth's orbit, so we see most of the Sun's north pole in September and most of its south pole in March each year. The Sun's "surface" that is visible, up to the photosphere. The powerful magnetic fields in the vicinity of sunspots produce active regions on the Sun that often generate disturbances such as solar flares and coronal mass ejections (CMEs). Because they are colder than their surroundings, sunspots seem "black.". The average number of spots on the face of the Sun is not constant, but varies over a multi-year cycle.

To learn more about North pole click here https://brainly.com/question/16270877

#SPJ4

Image distance changes with change in object distance.

What is object and image distance?

The object distance is the distance of the object to the center line of the lens

The image distance is the distance of the image to the center line of the lens

Now lets discuss the image variation with change in distance:

As the distance  between an object and a lens is increased, the image size decreases. This is due to the fact that the light rays from the object are diverging more at a greater distance, and thus the lens is not able to focus them as much. The result is a smaller image.

Moving the object further from the lens causes the image to become smaller and closer to the lens. The image becomes smaller and smaller as we move the object further and further away. It will move closer and closer to the focal point of the image as it approaches.

A lower distance between an object and a lens can increase the size of an image.

In other words, as the object distance decreases , the image distance increases; in other words, the image height rises as well.

When the distance of an object from one’s eye is increased, the image distance remains the same as the original size of the image.

To know more about image and object distance click the link:

brainly.com/question/14649723

#SPJ4

____________________________________________________

We are given the following:

Given the formula for finding acceleration, we fill in the blanks.

[tex]A=14.35*13.29[/tex]

[tex]A=190.7115=190.7[/tex] ← Acceleration/Final Solution

_____________________________________________________

Hope this helps!

The Inductance and Inductive Reactance of the conductor is 1.315 x 10⁻⁶H/m and 0.496ohm/km respectively.

The mathematical illustration of XL is shown in the equation below.

XL = 2πfL.

        De=8.819m

        L= 2 x 10⁻⁷ x log [8.819/0.0123]

        L=1.315 x 10⁻⁶H/m

            =0.496ohm/km

To find more about Inductive Reactance-

https://brainly.com/question/17129912

#SPJ4