Physics: Chapter 8

Question 1

Define momentum

Answer 1

the mass of an object multiplied by its velocity; momentum = inertia in motion

Question 2

If a small car and a large car have the same speed, which has more momentum?

Answer 2

large car

Question 3

If a car doubles its speed, what happens to its momentum?

Answer 3

it doubles

Question 4

What is equal to change in momentum?

Answer 4

impulse

Question 5

Why are padded dashboards used?

Answer 5

to delay the time of impact (decreases force of impact by increasing time)

Question 6

If a cannon fires a cannonball, how does the force on the ball compare to the force on the cannon?

Answer 6

equal and opposite

Question 7

If you are on ice and throw something, what happens to you?

Answer 7

same force pushes on you in opposite direction

Question 8

What happens to momentum when the mass is doubled?

Answer 8

(mass x velocity)momentum 2x

Question 9

Why is the recoil speed of a cannon so much smaller than the speed of the cannonball? When would the speeds be the same?

Answer 9

cannon has larger mass; same speed if they had the equal mass

Question 10

Why do you put your hand out in front of you to catch a ball?

Answer 10

to delay time of impact

Question 11

If a car hits another car at rest with the mass and they link together, what is the relationship between the initial speed of the 1st car and the speed of the 2 cars linked together?

Answer 11

half the speed

Question 12

What exerts the force on a rocket to make it move?

Answer 12

exhaust

Question 13

If you are in space and you throw something with more mass than you, which will have the greater speed, the object or you?

Answer 13

you

Question 14

If a 2kg object moves at 6m/s, find its momentum.

Answer 14

6m/s X 2kg = 12kg m/s

Question 15

If a 6kg ball has 90kg m/s of momentum, what is its speed?

Answer 15

90kg m/s / 6 m/s = 15kg

Question 16

If a ball moving at 5m/s has a momentum of 60kg m/s, what is its mass?

Answer 16

60kg m/s / 5 m/s = 12kg

Question 17

When a bug hits the windshield of a moving car, describe the forces, impulses, momentum changes, and accelerations of the bug and the car.

Answer 17

force = equal and opposite
momentum = equal and opposite but has more acceleration
impulse = equal and opposite

Question 18

Why do fighter’s ride with a punch?

Answer 18

counteracts the momentum of the punch, reduces force

Question 19

If a 30kg object moves 500m in 25 seconds, find the momentum.

Answer 19

500m / 25 sec = 20m/s

30kg x 20m/s = 600km m/s

Question 20

If a 3kg block moving 9m/s comes to a stop in 3 seconds, find the force.

Answer 20

f x 3 = 3(0-9)
f x 3 = -27
f = -9N

Question 21

If a 12kg object moving at 8m/s hits a 9kg block at rest and they stick together, what is their speed afterwards?

Answer 21

(12 x 8) + (9 x 0) = (12 + 9)VF
96 + 0 = (21)Vf
46 = Vf

Question 22

If a 30kg object moving at 8m/s hits a 20kg object moving towards it at 6m/s and they stick together, what is their speed afterwards?

Answer 22

(30 x 8) + (20 x -6) = (30+20)Vf
240 + -120 = (50)Vf
120 = 50Vf
24 = Vf

Question 23

If a 20kg ball moving at 3m/s bounces off a spring at about the same speed it had before in the opposite direction, what is its change in momentum?

Answer 23

~V

(3 - -3) = 6

Question 24

If a car moving at 57m/s is 5x more massive than the car it hits that is at rest, what is their speed afterwards if they lock together?

Answer 24

~P = M~V
5(57) + 1(0) = (5+1)Vf
285 + 0 = 6Vf
47.5 = Vf

Question 25

A 45kg girl and a 68kg boy are at rest on roller skates. The girl pushes the boy who moves away at 4m/s. What is the girl’s speed?

Answer 25

M1Vf1 = -M2Vf2
(45 x 0) = - (68kg x 4m/s)
Vf1 = 6.04