Physics Chapter 7 Reading Quiz

A machine puts out 100 J of work for every 1000 J of work put into it. The efficiency of the machine is (A) 10% (B) 50% (C) 90% (D) 110%

(A) 10%

A 2 kg mass held 4 m above the ground has 78.4 joules of gravitational potential energy. Once it is released, what's its speed in meters/second just before it hits the ground? Let g=9.8 m/s/s. All answers are rounded to the 1st decimal place. (A) 8.9 (B) 9.8 (C) 39.2 (D) 78.4 (E) none of these values

(A) 8.9

A rifle, at rest in outer space, is fired by remote control. Because of this, it recoils so that the bullet and the rifle are set in motion. The rifle is 120 times more massive than the bullet. Keeping in mind that the bullet will move away from the rifle at over 280 m/s, the rifle and the bullet ideally acquire equal (A) but opposite amounts of momentum. (B) amounts of kinetic energy. (C) amounts of both of these. (D) amounts of neither of these.

(A) but opposite amounts of momentum.

A ball is projected into the air with 100 J of kinetic energy. This kinetic energy is transformed to gravitational potential energy at the top of its trajectory. When the ball returns to its original level after encountering air resistance, its kinetic energy is (A) less than 100 Joules (B) more than 100 Joules (C) 100 Joules (D) not determinable, not enough information given.

(A) less than 100 Joules

An object that has kinetic energy must be (A) moving. (B) falling. (C) at an elevated position. (D) at rest. (E) none of these.

(A) moving.

An object is raised above the ground gaining a certain amount of potential energy. Raise the same object twice as high and it gains (A) twice as much potential energy.(B) four times as much potential energy. (C) neither of these amounts of potential energy.

(A) twice as much potential energy.

You push an object over a distance with a certain force. If you push the same object twice as far while applying the same force, you do (A) twice as much work. (B) four times as much work. (C) the same amount of work.

(A) twice as much work.

It takes 40 J to push a large box 4 meters across the floor. Assuming the push is in exactly the same direction as the movement of the box, what is the magnitude of the average force on the box? (A) 4 N (B) 10 N (C) 40 N (D) 160 N (E) none of these

(B) 10 N

A 1000 J of work is done to raise a toy elevator from the ground floor to the second floor in 20 seconds. How much power does the elevator use? (A) 20 W. (B) 50 W. (C) 1000 W. (D) 20,000 W.

(B) 50 W.

If an object has kinetic energy, then it also must have (that is, must possess) (A) an impulse. (B) momentum. (C) acceleration. (D) a force. (E) none of these.

(B) momentum.

A job is done slowly, while an identical job is done quickly. Both jobs require the same amount of work, but different amounts of (A) energy (B) power (C) both of these (D) neither of these.

(B) power

Two identical arrows, one with twice the kinetic energy of the other, are fired into a hay bale. The hay bale exerts a constant (unchanging) frictional force on the arrows as they move through the hay. The faster arrow will penetrate (A) the same distance as the slower arrow. (B) twice as far as the slower arrow. (C) four times as far as the slower arrow. (D) more than four times as far as the slower arrow.

(B) twice as far as the slower arrow.

A bow is drawn so that it has 40 J of potential energy. After leaving the bowstring, the arrow will ideally have a kinetic energy of (A) less than 40 J. (B) more than 40 J. (C) 40 J.

(C) 40 J.

A feather and a coin dropped in a vacuum fall with equal (A) forces (B) momenta (C) accelerations (D) kinetic energies

(C) accelerations

Two identical arrows, one with twice the speed of the other, are fired into a hay bale. The hay bale exerts a constant (unchanging) frictional force on the arrows as they move through the hay. The faster arrow will penetrate (A) the same distance as the slower arrow. (B) twice as far as the slower arrow. (C) four times as far as the slower arrow. (D) more than four times as far as the slower arrow.

(C) four times as far as the slower arrow.

No work is done by the force of gravity on a bowling ball that rolls horizontally along a bowling alley because (A) no force acts on the ball. (B) no distance is covered by the ball. (C) no part of the force of gravity is along the same line as the direction of the motion of the ball. (D) all of the force of gravity is along the same line as the direction of motion of the ball. (E) its kinetic energy remains constant.

(C) no part of the force of gravity is along the same line as the direction of the motion of the ball.

You push an object with a certain amount of work input over a certain time interval. If you push the same object with twice the work input for twice the time, your power input is (A) twice as much as the original amount. (B) four times as much as the original amount. (C) the same amount as for half the work in half the time.

(C) the same amount as for half the work in half the time.

A 50 kg sack is lifted 2 meters in the same time as a 25 kg sack is lifted 4 meters. The power used in raising the 50 kg sack compared to the power used to lift the 25 kg sack is (A) twice as much. (B) half as much. (C) the same amount.

(C) the same amount.

A 1000 kg car and a 2000 kg car are hoisted the same distance in a gas station. Raising the more massive car requires (A) less work. (B) as much work. (C) twice as much work. (D) four times as much work. (E) more than 4 times as much work.

(C) twice as much work.

A car moves 4 times as fast as another identical car. Compared to the slower car, the faster car has (A) 4 times the KE (B) 8 times the KE (C) 12 times the KE (D) 16 times the KE

(D) 16 times the KE

A moving object has (A) speed (B) velocity (C) momentum (D) energy (E) all of these.

(E) all of these.

When a car is braked to a stop, its kinetic energy is transformed into (A) stopping energy. (B) potential energy. (C) energy of motion (D) energy of rest. (E) heat energy.

(E) heat energy.

The efficiency of a car that takes every 40 joules of chemical potential energy in gasoline and converts it into 2 joules of useful kinetic energy is _____ percent.

5%

The amount of work done on an object can tell us how much ______ has been given to or taken away from it.

Energy

The specific kind of energy that an object has because of its height above the ground is called _____ _____ energy (2 words...1st word starts with a "G" and the second word starts with a "P")

Gravitational Potential

The metric unit, Newton-Meter, has another name to honor the person who helped to developed our basic understanding of the concepts in this chapter. This metric unit is called the ______ (Answer using a single word. Do not use a symbol.

Joule

The kind of energy associated with the motion of an object is called ______ energy. (1 word)

Kinetic

When you apply a force over a distance to slow down or stop an object, you do ______ work on it.(Hint: Answer starts with a "n")

Negative

The metric unit for work is the _____•_____ (answer with 2 words, not symbols).

Newton-Meter

When you cock a spring on a mousetrap, you do_____ work on the spring.(Hint: Answer starts with a "p")

Positive

You givean object energy by doing ______ (positive, negative) work on it.

Positive

The name for the amount of work done or energy used, or transformed, per unit of time is called _______.

Power

The unit of_____ is called the watt and is composed of the units_____ per _____.

Power, Joules, Second

The kind of energy used by a little toy car powered by a mouse trap is called _____ _____ energy (2 words...1st word starts with a "S" and the 2nd word starts with a "P")

Spring Potential

Momentum is a _____ quantity, while work and energy are "directionless" and are therefore _____ quantities.

Vector, Scalar

In its simplest sense, the _____ done on an object is equal to the product of force and distance.

Work