### All GRE Subject Test: Physics Resources

## Example Questions

### Example Question #14 : Friction And Normal Force

A block rests on a wooden table with a coefficient of kinetic friction equal to . A spring scale attached to the right side of the block is very gently pulled to the right with increasing force. If the spring scale is pulled with a force of , what is the acceleration of the system?

**Possible Answers:**

**Correct answer:**

The force of kinetic friction is given by the equation:

We can calculate the frictional force using the values from the question.

There are four force acting on the block: force from gravity, normal force, force of the spring scale, and force of friction. The normal force will be equal and opposite to the force of gravity, allowing us to cancel the forces in the vertical direction. This leaves us with a net force calculation for the horizontal force: the spring scale force and the force of friction. Note that the frictional force remains negative, as it acts in the opposite direction to the spring scale force.

Now that we know the net force and the mass of the block, we can calculate the acceleration using Newton's second law.

### Example Question #2 : Electric Fields

Which of the following equations best relates capacitance, charge, and distance between parallel plates as they pertain to the electric field, ?

**Possible Answers:**

**Correct answer:**

This question forces us to combine two equations.

Using substitution, we can solve for the electric field with the variables given in the question stem.

### Example Question #571 : Mcat Physical Sciences

A circuit consists of a current passing through a resistor for . Find the heat generated.

**Possible Answers:**

**Correct answer:**

Ohm's Law states that . We are given the current and resistance, allowing us to solve for the voltage.

We also know that . Now that we have the voltage, we can solve for the power.

Finally, we know that . Using this, we can solve for the energy (or work) that is generated by the circuit.

### Example Question #191 : Ap Physics 2

What is the magnitude of force on a charge travelling at a constant velocity of through a perpendicular magnetic field?

**Possible Answers:**

**Correct answer:**

The equation for finding the force on a charge in a magnetic field is

*F = qvBsinθ *

Where q is charge in coulombs, v is the velocity of the charge, and B is the strength of the magnetic field in Teslas. Since the charge is moving perpendicular to the magnetic field, sinθ =1. Therefore we solve for force by plugging in the values and multiplying.

### Example Question #11 : Optics

A man stands ten meters away from a converging mirror with a focal length of two meters. What is true of the image he sees?

**Possible Answers:**

His image is virtual, upright, and minimized

His image is real, upright, and magnified

His image is virtual, upright, and magnified

His image is real, inverted, and minimized

His image is real, inverted, and magnified

**Correct answer:**

His image is real, inverted, and minimized

The first thing to consider when answering this question is the fact that real images are always inverted and virtual images are always upright. Once you have determined one or the other, two answer choices can be eliminated.

The first equation that is necessary for this question is .

From this we can determine that is equal to . Since is a positive number we know the image is real, and thus inverted.

The second equation to consider is for magnification: .

If the absolute value of is greater than one, the image is magnified, and if the value is less than one, it is minimized.

We would expect the image to be minimized.

### Example Question #4 : Mirrors And Lenses

A virtual image is formed from a convex mirror with a focal length of . How far from the mirror is the object that created this image?

**Possible Answers:**

**Correct answer:**

Use the equation:

Focal length is negative for convex mirrors, and image distance is negative for virtual images. We are given these values in the question, allowing us to calculate the object distance.

### Example Question #7 : Light And Electromagnetic Waves

A ray of light strikes the surface of a pond at an angle of to the vertical. If it is moving from air to water, what will be the angle of refraction?

**Possible Answers:**

**Correct answer:**

For this problem, use Snell's law: .

In this equation, is the index of refraction and is the angle of refraction to the vertical. Using the values given in the question, we can find the resultant angle of refraction.

Take the arcsin of both sides to find the value of .

### Example Question #1 : Gre Subject Test: Physics

A new crystal is discovered with an index of refraction of . What is the speed of light in this crystal?

**Possible Answers:**

**Correct answer:**

The relationship between speed of light and the index of refraction is:

In this formula, is the speed of light in a vacuum, is the observed speed of light in the substance, and is the index of refraction. We are given the speed of light in a vacuum and the index of refraction, allowing us ot solve for the speed of light in the crystal.

### Example Question #3 : Centripetal Force And Acceleration

What is the centripetal force on a ball being swung in a vertical loop with a velocity of on a string?

**Possible Answers:**

**Correct answer:**

Centripetal force is given by the equation:

The length of the string represents the radius of the circle being formed. Use the given string length as the radius, along with the mass of the ball and the velocity, to calculate the centripetal force.

### Example Question #4 : Work, Energy, And Power

How much work is done to lift a block to a point above its resting location?

**Possible Answers:**

**Correct answer:**

The work done is equal to the gravitational potential energy of the block after it has been lifted.

The gravitational potential energy is calculated using the following formula:

We are given the mass and the change in height, and we know the acceleration due to gravity. Using these values, we can solve for the change in potential energy by multiplication.

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