AP Physics 1 : Work, Energy, and Power

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #61 : Newtonian Mechanics

Determine the kinetic energy of a mole of oxygen gas(atomic mass unit = 16Da) if each travels at speed of 

 

Possible Answers:

Correct answer:

Explanation:

First, let's remember what it means to have  mole of an atom given its atomic mass unit in Daltons.  mole of oxygen with atomic mass of  is going to be  grams. In kilograms, this would be:

 

Plugging this into the equation for kinetic energy 

, where  is the mass,  is its velocity. 

For this problem,  and 

Therefore,

Example Question #11 : Kinetic Energy

A block with a mass of  is dropped from a height and just before it hits the ground, it has a velocity of . From what height was the block dropped from?

Possible Answers:

Correct answer:

Explanation:

Just before impact, the block has maximum kinetic energy. Once the kinetic energy is determined, we can find the potential energy and therefore the height of the drop. We can use the following formula to determine the kinetic energy:

All of this energy was previously potential energy from which we can determine the height, .

Example Question #63 : Work, Energy, And Power

A soccer ball of mass 0.5kg is kicked and accelerated uniformly from rest to travel 20 meters over 3 seconds into the goal. What is the final kinetic energy of the soccer ball?

Possible Answers:

Correct answer:

Explanation:

We need to know the final speed of the ball since we have all but this quantity in our formula for kinetic energy, 

To find the final velocity we first find the acceleration: 

Example Question #64 : Work, Energy, And Power

A champagne cork with a mass of 10 grams accelerates off the top of the champagne bottle at  for 2 seconds. What is the final kinetic energy of the cork after 2 seconds?

Possible Answers:

Correct answer:

Explanation:

We can find the final velocity by multiplying the acceleration by the time. We then plug this into the formula for kinetic energy and solve. Do not forget to convert grams to kilograms.

The initial velocity of the cork was zero.

Example Question #61 : Work, Energy, And Power

In an investigation into energy, a student compresses a spring a distance of  from its neutral length. She then puts a cart against the end of the spring and releases both the spring and the cart. She measures the kinetic energy of the cart after the spring has returned to its neutral length and finds it to be . She then repeats the experiment, but this time compresses the spring a distance of  before releasing the spring and the cart. What would the cart's kinetic energy be in the second experiment?

Possible Answers:

Correct answer:

Explanation:

The potential energy stored in a spring is given by

So the energy increases with the square of the compression. When the potential energy is converted to kinetic energy of the cart, it increases by a factor of .

Example Question #61 : Newtonian Mechanics

In an investigation into energy, a student compresses a spring a distance of  from its neutral length. She then puts a cart against the end of the spring and releases both the spring and the cart. She measures the velocity of the cart after the spring has returned to its neutral length and finds it to be . She then repeats the experiment, but this time compresses the spring a distance of  before releasing the spring and the cart. What would the cart's velocity be in the second experiment?

Possible Answers:

Correct answer:

Explanation:

The potential energy stored in a spring is given by

So doubling the compression increases the potential energy by a factor of .  However, the kinetic energy:

, increases with the square of the velocity, so the velocity only needs to double to increase the cart's kinetic energy by a factor of .

Example Question #62 : Newtonian Mechanics

In an investigation into energy, a student compresses a spring a distance of  from its neutral length. She then puts a cart of mass  against the end of the spring and releases both the spring and the cart. She measures the velocity of the cart after the spring has returned to its neutral length and finds it to be . She then repeats the experiment, but this time using a cart whose mass is  before releasing the spring and the cart. What would the cart's velocity be in the second experiment?

Possible Answers:

Correct answer:

Explanation:

Kinetic energy is given by:

, so the energy is linearly dependent on the mass, but increases with the square of the velocity. So although the mass has doubled, the velocity only needs to decrease by a factor of  to maintain the same kinetic energy. In algebraic form:

Simplify.

Example Question #61 : Work, Energy, And Power

There is a truck and a car on a highway going the same speed in the same direction. The car has mass  while the truck has mass .

What is the correct statement about the two vehicle's kinetic energies?

Possible Answers:

The truck has four times the kinetic energy of the car

The car and the truck have the same kinetic energy

The car has double the kinetic energy of the truck

The car has exactly  the kinetic energy of the truck

The car has exactly  the kinetic energy of the truck.

Correct answer:

The car has exactly  the kinetic energy of the truck

Explanation:

The equation for kinetic energy is:

Where  is the mass of an object and  is the velocity of the object.

We see from the equation that mass has a linear relationship with kinetic energy and the problem statement gives that the vehicles have the same velocity. Because the car has half the mass of the truck and the same speed, the car has half as much kinetic energy as the truck.

Without specific numbers given, we can always substitute easy numbers into the equation to help understand the concept. If we say the velocity in both cases is , and the car's mass is  then we have:

We know the truck's mass is double the car's, which yields:

This makes it clear that the car has half the kinetic energy of the truck.

Example Question #69 : Work, Energy, And Power

Moment of inertia of hollow sphere:

A kickball of mass and radius is on top of a hill of height , at the edge of a straight incline to the bottom. Suppose the ball was just barely pushed over the edge. Calculate the ball's velocity at the bottom of the hill. It may be assumed that the ball is essentially hollow. Ignore any losses due to friction, as well as any velocity from the initial push.

Possible Answers:

Correct answer:

Explanation:

There will be two types on kinetic energy, rotational and translational.

Using conservation of energy:

Initially, kinetic energy will be zero, and in the final state, potential energy will be zero.

Recall:

and

Combine equations:

Solve for

Plug in values:

Example Question #70 : Work, Energy, And Power

Determine the kinetic energy of a mole of oxygen gas at 

The formula for kinetic energy given temperature is:

, where  is the number of moles, , and  is temperature. 

Possible Answers:

Correct answer:

Explanation:

To solve this question, we simply plug in given values into the equation for kinetic energy:

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