Question 1

Two objects of equal mass and velocity hit a wall. They both rebound with the same velocity in the opposite direction. Both objects experience the same momentum change but one experiences twice the average force as the other. Which of the following statements is true?

Accepted Answer

A)   The contact time between one of the objects and the wall is twice the contact time of the other.
B)   The contact times between the objects and the wall are equal.
C)   The contact time between one of the object and the wall is one-fourth the contact time of the other.
D)   The change in the kinetic energy is different for the two objects.
E)   The contact time between one of the objects and the wall is 1/3 the contact time of the other. A

Question 2

A 90 kg person is sitting in a 100 kg boat, which is floating at rest on a lake. In the boat is a stone with a mass of 5.0 kg. The person throws the stone at 4.0 m/s horizontally in the NORTH direction. The velocity of the person and the boat after throwing the stone is

Accepted Answer

A)   2.00 m/s NORTH.
B)   1.21 m/s SOUTH.
C)   1.21 m/s NORTH.
D)   0.11 m/s SOUTH.
E)   0.11 m/s NORTH. D

Question 3

A 100.0 kg mass, initially at rest, is blown apart into a 95.00 kg piece and a 5.000 kg piece. After the blast, the two masses are moving apart with a relative velocity of 100.0 m/s. The kinetic energy of the 5.000 kg mass after the explosion is

Accepted Answer

A)   6,850 J.
B)   7,500 J.
C)   9,570 J.
D)   11,500 J.
E)   22,560 J. E

Question 4

A 4.00 kg object is moving at 5.00 m/s EAST. It strikes a 6.00 kg object that is at rest. The objects collide elastically. The velocity of 4.00 kg object after the collision is in the SOUTHWEST direction. The speed of the 6.00 kg object after the collision is

Accepted Answer

A)   2.38 m/s.
B)   3.02 m/s.
C)   3.96 m/s.
D)   4.06 m/s.
E)   5.22 m/s.

Question 5

A 5.0 kg ball is traveling at 4.0 m/s and strikes a wall. The ball bounces off the wall with a velocity of 4.0 m/s in the opposite direction. If the ball is in contact with the wall for 0.10 seconds, then the magnitude of the impulse on the ball is

Accepted Answer

A)   24 kg m/s.
B)   30 kg m/s.
C)   36 kg m/s.
D)   40 kg m/s.
E)   50 kg m/s.

Question 6

A 3.00 kg object is moving at 5.00 m/s EAST. It catches up to and strikes a 6.00 kg that is moving EAST at 2.00 m/s. The objects undergo an elastic collision in the EAST-WEST direction. The velocity of the 3.00 kg object after the collision is

Accepted Answer

A)   4.00 m/s EAST.
B)   1.00 m/s EAST.
C)   4.00 m/s WEST.
D)   1.00 m/s WEST.
E)   3.00 m/s EAST.

Question 7

An 1800 kg car traveling at 35.0 m/s strikes a wall. If the car comes to rest in 0.500 seconds, then the magnitude of the average force of the wall on the car is

Accepted Answer

A)   0.330 × 105 N.
B)   0.640 × 105 N.
C)   1.26 × 105 N.
D)   2.77 × 105 N.
E)   3.33 × 105 N.

Question 8

A 3.00 kg mass and a 4.00 kg mass are dropped from a great height simultaneously. What is the magnitude of the velocity of the center of mass at t = 10 s (ignore air resistance)?

Accepted Answer

A)   9.8 m/s
B)   7.0 m/s
C)   70 m/s
D)   98 m/s

Question 9

A 4.00 kg mass is moving at 4.00 m/s 45.0 degrees NORTH of WEST and a 6.00 kg mass is moving at 3.00 m/s 30.0 degrees SOUTH of EAST. Find the velocity of the center of mass, letting (a) = the east-west component, and (b) = the north-south component.

Accepted Answer

A)   a = 0.427 m/s, b = 2.31 m/s.
B)   a = 1.23 m/s, b = 0.231 m/s.
C)   a = 0.427 m/s, b = 0.231 m/s.
D)   a = 1.73 m/s, b = 1.43 m/s.
E)   a = 0.427 m/s, b = 0.213 m/s.

Question 10

A model rocket with a mass of 750 grams is launched straight up. It achieves a speed of 25.0 m/s in 2.00 seconds. Ignoring any change in mass of the rocket due to expelled fuel, and neglecting air resistance, the magnitude of the average net force on the rocket is

Accepted Answer

A)   9.38 N.
B)   24.5 N.
C)   16.7 N.
D)   41.7 N.
E)   52.8 N.

Question 11

A pair of identical balls are connected by a massless rod, and thrown straight up into the air. The velocity of the center of mass is initially 17.2 m/s upward. Precisely 1.0 s later, one of the balls is measured to be instantaneously at rest. What is the velocity of the other ball at this time? Ignore air resistance.

Accepted Answer

A)   14.8 m/s up
B)   9.8 m/s down
C)   7.4 m/s up
D)   7.4 m/s down

Question 12

A 100 kg mass, initially at rest, is blown apart into a 90.0 kg piece and a 10.0 kg piece. After the blast, the two masses are moving apart with a relative velocity of 100 m/s. The speed of the 10.0 kg mass after the explosion is 90.0 m/s. The total kinetic energy of the two masses after the explosion is

Accepted Answer

A)   63,200 J.
B)   45,000 J.
C)   30,400 J.
D)   23,400 J.
E)   4,500 J.

Question 13

A 2200 kg truck slows down, reducing its momentum by 22000 kg·m/s in 3.2 s, as its driver sees a deer wander into the road. What is the magnitude of the average net force that slows the truck?

Accepted Answer

A)   8.3 kN
B)   23.4 kN
C)   6.9 kN
D)   15.1 kN

Question 14

A binary star system is composed of two stars (one blue, one red) that orbit a common center of mass. Let the distances from the stars to the center of mass be labeled rblue and rred. The sum of the masses of the stars is Mblue + Mred = 3.70 x 1033 kg. If it is known that rblue = 2/5 rred, what is Mred?

Accepted Answer

A)   1.06 × 1033 kg
B)   2.64 × 1033 kg
C)   1.48 × 1033 kg
D)   2.22 × 1033 kg

Question 15

A sticky hockey puck slides along a frictionless, horizontal ice surface at 75 m/s in the +x direction. It collides with a second sticky puck originally sliding at 25 m/s in the -y direction. They collide perfectly inelastically. If the first puck has a mass twice that of the second, what is the angle of their final velocity vector below the +x direction?

Accepted Answer

A)   37 degrees
B)   9.5 degrees
C)   49 degrees
D)   42 degrees
E)   34 degrees

Question 16

A 4.00 kg object is moving at 5.00 m/s NORTHWEST. It strikes a 6.00 kg object that is moving SOUTHWEST at 2.00 m/s. The objects collide perfectly inelastically (stick together). The velocity of the 6.00 kg object after the collision is

Accepted Answer

A)   2.33 m/s at an angle of 45.0 degrees NORTH of WEST.
B)   3.89 m/s at an angle of 35.0 degrees NORTH of WEST.
C)   3.89 m/s at an angle of 14.0 degrees NORTH of WEST.
D)   2.33 m/s at an angle of 14.0 degrees NORTH of WEST.
E)   2.33 m/s at an angle of 35.0 degrees NORTH of WEST.

Question 17

A 3.00 kg mass is located at x = 2.0 cm and y = 4.0 cm. A 3.00 kg mass is located at x = −5.0 cm and y = 2.0 cm. A 4.00 kg mass is located at x = 3.0 cm and y = −3.0 cm. Where is the center of mass (x, y)?

Accepted Answer

A)   (0.60 cm, 0.30 cm) 
B)   (0.90 cm, 2.0 cm) 
C)   (3.0 cm, 1.0 cm) 
D)   (0.30 cm, 0.60 cm) 
E)   (3.9 cm, 3.0 cm)

Question 18

A car accelerates from rest along a straight road, increasing its momentum from 0 to 52500 kg·m/s in 6.5 s. If its engine and tires are able to provide an average force of 8500 N, what is the magnitude of the net dissipative force (friction and air resistance) on the car during this interval?

Accepted Answer

A)   11450 N
B)   1840 N
C)   3510 N
D)   423 N

Question 19

A 1200 kg car is moving at 5.0 m/s EAST. It strikes an 1800 kg car at rest. The cars undergo an elastic collision and move in the EAST or WEST direction. The velocity of the 1200 kg car after the collision is

Accepted Answer

A)   4.0 m /s EAST.
B)   1.0 m/s EAST.
C)   4.0 m/s WEST.
D)   1.0 m/s WEST.
E)   3.0 m/s EAST.

Question 20

A 4.00 kg object is moving at 3.00 m/s WEST. It catches up to and strikes a 6.00 kg that is moving WEST at 2.00 m/s. The objects undergo an elastic collision in the EAST-WEST direction. The velocity of the 4.00 kg object after the collision is

Accepted Answer

A)   1.00 m/s WEST.
B)   2.80 m/s EAST.
C)   1.80 m/s WEST.
D)   2.80 m/s WEST.
E)   1.80 m/s EAST.

Exam 7: Linear Momentum