chapter5

Question 1

How many forces are required for an interaction?

Answer 1

Two forces, an action and a reaction, are needed for an interaction

Question 2

A Volkswagen Bug and a Volvo truck have a head-on collision. Which statement is true??

Answer 2

The magnitudes of both forces are the same

Question 3

Earth pulls down on you with a gravitational force that you call your weight. Do you pull up on Earth with the same amount of force?

Answer 3

Yes, you pull up on Earth with the same force

Question 4

If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?

Answer 4

Remember F = ma, and note that the cannon has a much greater mass than the cannon ball, so the cannon accelerates less for the same force.

Question 5

Can you physically touch a person without that person touching you with the same amount of force?

Answer 5

No, when you touch a person, they must touch you with an equal and opposite force

Question 6

How does the magnitude of the vertical component of velocity for a ball tossed at an upward angle change as the ball travels upward? How about the horizontal component of velocity when air resistance is negligible?

Answer 6

The vertical component decreases in magnitude until it reaches the maximum height and then increases; the horizontal component is constant.

Question 7

When a boxer hits a punching bag, the strength of his punch depends on how much force the bag can

Answer 7

exert on the boxer’s fist

Question 8

Your friend says that the heavyweight champion of the world cannot exert a force of 50 N on an isolated piece of tissue paper with his best punch. You

Answer 8

agree that it can’t be done

Question 9

When you walk, you push on the floor to the left and the floor

Answer 9

pushes you to the right

Question 10

Harry pulls on the end of a spring attached to a wall. The reaction to Harry’s pull on the spring is

Answer 10

the spring pulling on Harry

Question 11

Action and reaction pairs of forces

Answer 11

always act simultaneously

Question 12

For every action force, there must be a reaction force that

Answer 12

is equal in magnitude

Question 13

To produce an acceleration to a system there

Answer 13

must be a net force on the system

Question 14

While you stand on the floor you are pulled downward by gravity, and supported upward by the floor. Gravity pulling down and the support force pushing up

Answer 14

do not make an action-reaction pair of forces.

Question 15

The force exerted on the tires of a car that directly accelerate it along a road is exerted by the

Answer 15

road

Question 16

Neglecting air resistance, once a tossed ball leaves your hand

Answer 16

only the force due to gravity acts on it.

Question 17

An automobile and a golf cart traveling at the same speed collide head-on. The impact force is

Answer 17

the same for both.

Question 18

A Mack truck and a Volkswagen traveling at the same speed have a head-on collision. The vehicle that undergoes the greatest change in velocity will be the

Answer 18

Volkswagen

Question 19

As a ball falls, the action force is the Earth’s pull on the ball. The reaction force is the

Answer 19

ball’s pull on Earth

Question 20

The force with which Earth pulls on the Moon is

Answer 20

equal in magnitude to the force that Moon pulls on Earth

Question 21

When a cannonball is fired from a cannon, which undergoes the greater acceleration?

Answer 21

the cannonball

Question 22

The force that propels a cannonball when fired from a cannon is

Answer 22

equal and opposite to the force the ball exerts on the cannon

Question 23

When a rocket forces exhaust gases downward, the exhaust gases

Answer 23

exert an upward force on the rocket

Question 24

An astronaut of mass 70 kg weighs 700 N on Earth’s surface. His weight on the surface of Mars, where the acceleration due to gravity is 3.7 m/s2, would be about

Answer 24

260 N

Question 25

You stand on your skateboard and exert a 50-N push on the wall next to you. If your mass is 60 kg you’ll momentarily accelerate from the wall at about

Answer 25

0.8 m/s2

Question 26

When Nellie hangs suspended from a pair of ropes that are not vertical, the tension in each rope is

Answer 26

more than half her weight

Question 27

Nellie tosses a ball upward at an angle. Neglecting air resistance, the horizontal component of the initial velocity

Answer 27

remains constant

Question 28

Nellie tosses a ball upward at an angle. Neglecting air resistance, the vertical component of the initial velocity

Answer 28

decreases with time to reach the top

Question 29

The airspeed of an airplane is 200 km/h. When it is caught in a 200-km/h crosswind, its speed across the ground below is

Answer 29

283 km/h

Question 30

A river 100 m wide flows due south. A boat that goes 1 m/s relative to the water is pointed due east as it crosses from the west bank. The boat crosses in

Answer 30

100 s

Question 31

A river 100 m wide flows due south at 1 m/s. A boat that goes 1 m/s relative to the water leaves the west bank. To land at a point due east of its starting point, the boat must be pointed

Answer 31

nowhere it can’t be done.

Question 32

Why does the vertical component of velocity for a projectile change with time, whereas the horizontal component of velocity doesn’t change?

Answer 32

Gravity is a purely vertical force

Question 33

A stone is thrown upward at an angle. What happens to the horizontal component of its velocity as it rises? As it falls?

Answer 33

Rising or falling, it does not change.

Question 34

A stone is thrown upward at an angle. What happens to the magnitude of the vertical component of its velocity as it rises? As it falls?

Answer 34

It decreases while rising, but it increases while falling

Question 35

A ball rolls off the edge of a table at the same time another ball drops vertically from the same table. The ball to hit the floor first is the

Answer 35

both hit at the same time

Question 36

As soon as a bowling ball rolls off the edge of a table its horizontal component of velocity

Answer 36

remains constant.

Question 37

A Texas State Bobcat tosses a ball at an angle to the horizon such that the vertical component of velocity is 30 m/s and the horizontal component of velocity is 20 m/s. Neglect air resistance. About how far from the student does the ball land?

Answer 37

120 m

Question 38

A vertical vector of 3 units combined with a horizontal vector of 4 units has a resultant of

Answer 38

5 units