Unit 5 Practice Test

Question 1

Which of the following is the momentum of a 10 g ball moving at 2 m / s?

Answer 1

0.02 kg m / s

Question 2

A 10 g ball is thrown with a speed of 2 m / s at a wall. It bounces off the wall with a speed of 2 m / s. Assume that the ball was in contact with the wall for 0.01 s. How much force did the ball exert on the wall?

Answer 2

4 N

Question 3

A small rocket that is lifting off vertically loses 100 kg of fuel per second and is moving at a constant velocity of 50 m / s. How much force is the engine exerting?

Answer 3

5,000 N

Question 4

To determine the amount of impulse imparted to a 1 g golf ball after it is hit for 0.01 s by a 1 kg golf club, you must know __________________.

Answer 4

the velocity of the golf ball after impact

Question 5

A car moving at 30 m / s (108 mph) crashes into a brick wall, and the 80 kg driver comes in contact with the steering wheel for 0.01 s. How much force does the driver experience?

Answer 5

240,000 N

Question 6

A 30 kg concrete block falls 50 m to the ground where it makes contact for 0.1 s. How much force does the block exert on the ground when it lands?

Answer 6

9,391 N

Question 7

A baseball player hits a 30 m / s pitch back to the pitcher at 35 m / s. Assuming that the baseball has a mass of 0.4 kg, how much impulse did the player give the ball?

Answer 7

26 kg(m / s)

Question 8

A 60 kg bumper car coasting at a speed of 5.0 m / s crashes into another bumper car of mass 50 kg, moving at a speed of 2.0 m / s in the same direction. Immediately after the collision, the speed of the first car is 3.4 m / s (in the same direction as before). What is the speed of the second car?

Answer 8

3.9 m/s

Question 9

Momentum is conserved when ________________.

Answer 9

the net external force is zero

Question 10

A 120 kg astronaut in space throws a 2 kg wrench at a velocity of 3 m / s. How fast and in which direction does the astronaut move?

Answer 10

0.05 m / s in the opposite direction of the wrench

Question 11

Two carts on an airtrack (i.e., no friction), each with a mass of 3 kg, are moving to the right. Cart 1 has a speed of 0.5 m / s, and Cart 2 has a speed of 1.5 m / s and is following Cart 1. When the faster cart bumps into the slower cart, they stick together. How fast do the two carts move after this collision?

Answer 11

1.0 m/s

Question 12

A 2 kg object collides head-on with a 9 kg object moving 4 m / s to the right. The two objects stick together and the combined object is at rest. What is the velocity of the 2 kg object at the time of the collision?

Answer 12

−18 m / s

Question 13

If an 18-wheeler and a compact sedan collide head-on, which vehicle experiences a greater change in momentum?

Answer 13

They experience the same change in momentum.

Question 14

A spaceship is at rest in deep space. It fires its rocket so that in 1 s 1/120 of its mass is ejected with an exhaust speed of 2,400 m / s. Which of the following is the spaceship’s initial acceleration?

Answer 14

+20 m / s2

Question 15

A rocket starts off at rest and has 1/4 of its initial mass as fuel. If all the fuel is burned up in 90 s, and the exhaust velocity is 2,400 m / s, what is the final speed of the rocket?

Answer 15

690.4 m / s

Question 16

The initial mass of a rocket and its fuel is 6,000 kg. Its exhaust velocity is 2,000 m / s. How much gas must be ejected in the first second of burning to have an acceleration of 25 m / s2?

Answer 16

75 kg

Question 17

A collision is elastic if __________.

Answer 17

the total kinetic energy is conserved

Question 18

A 1,500 kg car traveling east at 10 m / s collides with a 1,000 kg truck traveling west at 20 m / s. The car and the truck stick together after the collision. Which of the following is their common velocity after the collision?

Answer 18

2 m / s; west

Question 19

In a two-body collision, total momentum will be conserved if, and only if, ___________.

Answer 19

the net external force acting on the two-body system is zero

Question 20

A 150 g golf ball sitting on a tee at rest is struck by a golf club. The total time the club and ball are in contact with each other is 0.006 s. If the ball moves away from the club at 30 m / s, what is the net force exerted by the club on the ball?

Answer 20

750 N

Question 21

A ballistic pendulum is a pendulum consisting of a large block of material hanging by a string. Bullets are fired into the block, causing the pendulum to swing. If a bullet with a mass of 20g is fired 250 m/s into a wood block with a mass of 2.0 kg, how fast will the combined bullet-block mass move immediately after the collision?

Answer 21

2.48 m / s

Question 22

A block with a mass of 2 kg slides along a frictionless, horizontal surface with a speed of 2 m / s. It collides with a second block of mass 4 kg, which is sitting at the base of a 30° frictionless incline. The two blocks collide inelastically. What is the vertical height that the two blocks will slide up the incline?

Answer 22

2.3 cm

Question 23

Two clay balls roll toward each other and collide head-on. One ball has a mass of 0.5 kg and moves to the left with an initial speed of 2 m / s. The other ball moves to the right with an initial speed of 3 m / s. The two balls stick together upon colliding with each other. The combined mass moves to the right with a speed of 1.5 m / s. What is the mass of the second ball?

Answer 23

1.2 kg

Question 24

A model rocket is shot straight up in the air, and at its highest point explodes into two unequal pieces. The smaller piece, of mass 5 kg, moves straight down after the explosion at an initial speed of 20 m / s. How much higher does the larger piece, of mass 10 kg, travel? Assume the acceleration of gravity is 10 m / s2.

Answer 24

5 m

Question 25

Two cars collide inelastically at an intersection. The two cars have identical masses, m, but one is driving twice as fast as the other. The incident angle is 90°. Which of the following is the velocity of the combined cars after the collision?

Answer 25

vf = 1.1vi; theta = 63 degrees