Question 1

A soccer player kicks a ball with a force of 1500 N. According to Newton's third law, what is the magnitude of the force exerted by the ball on the player's foot?

Accepted Answer

1500 N

Question 2

When you step off a curb, Earth pulls you downward with a force equal to your weight. What is the reaction force according to Newton's third law?

Accepted Answer

You pulling Earth upward

Question 3

A cannonball and a cannon experience equal and opposite forces when fired. Why does the cannonball accelerate more than the cannon?

Accepted Answer

The masses are different

Question 4

Two people of equal mass push off from each other on slippery ice. What will happen to their speeds?

Accepted Answer

Both will move at the same speed in opposite directions

Question 5

A bird flies by pushing air downward. According to Newton's third law, what is the result of this action?

Accepted Answer

The air pushes the bird upward

Question 6

If the speed of an object is doubled, what happens to its momentum?

Accepted Answer

Doubles

Question 7

A fast-moving car hits a haystack or a cement wall. In both cases, the car comes to rest. Which statements are true?

Accepted Answer

Yes for change in momentum and impulse, but not force

Question 8

A moving object has mass $$m$$ and velocity $$v. $$What is its momentum?

Accepted Answer

$$p = mv$$

Question 9

A freight car A of mass $$m$$ moving at speed $$v$$ collides and couples with identical freight car B at rest. What is the speed of the coupled cars after collision?

Accepted Answer

$$\frac{v}{2}$$

Question 10

A worker lifts a 20-N box to a shelf 2 meters high. How much work is done?

Accepted Answer

$$W = 40 	ext{ J}$$

Question 11

A car with mass $$m is $$moving at speed $$v. $$What is its kinetic energy?

Accepted Answer

$$KE = \frac{1}{2}mv^2$

Question 12

If the initial speed of a car is doubled, how does the stopping distance change, assuming the same friction force?

Accepted Answer

It is quadrupled

Question 13

A machine is 30% efficient. If you input 100 J of energy, how much is converted to useful work?

Accepted Answer

30 J

Question 14

A woman uses an ideal pulley system to lift a 100-N crate by pulling a rope downward with a force of 25 N. For every 1-meter length of rope she pulls, how far does the crate rise?

Accepted Answer

25 centimeters

Question 15

Which equation expresses the work-energy theorem?

Accepted Answer

$$W = \Delta KE$$

Question 16

A helicopter moves upward when lift is greater than its weight. Which force is responsible for this upward motion?

Accepted Answer

Lift

Question 17

A crate is lifted by a pulley to a height $$h. $$What is its increase in gravitational potential energy?

Accepted Answer

$$PE = mgh$$

Question 18

A moving boulder has more momentum than a stone rolling at the same speed. Why?

Accepted Answer

The boulder has more mass

Question 19

Which of the following best describes the law of conservation of energy?

Accepted Answer

Energy may be transformed, but the total amount never changes

Question 20

A firecracker explodes into several pieces. What is true about the vector sum of the momenta of the pieces after the explosion?

Accepted Answer

It is equal to the initial momentum

Forces, Newton's Laws, Momentum, and Energy: Mini-Textbook Study Notes

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