Question 1

The only force acting on a 2.0-kg object moving along the x axis is shown.If the velocity vx is +2.0 m/s at t = 0,what is the velocity at t = 4.0 s?

Accepted Answer

A)  +4.0 m/s
B)  +5.0 m/s
C)  +6.0 m/s
D)  +7.0 m/s
E)  +2.0 m/s A

Question 2

A 3.00-kg stone is dropped from a 39.2 m high building.When the stone has fallen 19.6 m,the magnitude of the impulse it has received from the gravitational force is

Accepted Answer

A)  9.80 N  s.
B)  19.6 N  s.
C)  29.4 N  s.
D)  58.8 N  s.
E)  118 N  s. D

Question 3

A 6.0-kg object moving 5.0 m/s collides with and sticks to a 2.0-kg object.After the collision the composite object is moving 2.0 m/s in a direction opposite to the initial direction of motion of the 6.0-kg object.Determine the speed of the 2.0-kg object before the collision.

Accepted Answer

A)  15 m/s
B)  7.0 m/s
C)  8.0 m/s
D)  23 m/s
E)  11 m/s D

Question 4

The value of the momentum of a system is the same at a later time as at an earlier time if there are no

Accepted Answer

A)  collisions between particles within the system.
B)  inelastic collisions between particles within the system.
C)  changes of momentum of individual particles within the system.
D)  internal forces acting between particles within the system.
E)  external forces acting on particles of the system.

Question 5

At the instant a 2.0-kg particle has a velocity of 4.0 m/s in the positive x direction,a 3.0-kg particle has a velocity of 5.0 m/s in the positive y direction.What is the speed of the center of mass of the two-particle system?

Accepted Answer

A)  3.8 m/s
B)  3.4 m/s
C)  5.0 m/s
D)  4.4 m/s
E)  4.6 m/s

Question 6

A 1.0-kg object moving 9.0 m/s collides with a 2.0-kg object moving 6.0 m/s in a direction that is perpendicular to the initial direction of motion of the 1.0-kg object.The two masses remain together after the collision,and this composite object then collides with and sticks to a 3.0-kg object.After these collisions,the final composite (6.0-kg)object remains at rest.What was the speed of the 3.0-kg object before the collisions?

Accepted Answer

A)  15 m/s
B)  10 m/s
C)  5.0 m/s
D)  20 m/s
E)  25 m/s

Question 7

Three particles are placed in the xy plane.A 40-g particle is located at (3,4)m,and a 50-g particle is positioned at (−2,−6)m.Where must a 20-g particle be placed so that the center of mass of this three-particle system is located at the origin?

Accepted Answer

A)  (−1,−3) m
B)  (−1,2) m
C)  (−1,12) m
D)  (−1,7) m
E)  (−1,3) m

Question 8

A 2.4-kg ball falling vertically hits the floor with a speed of 2.5 m/s and rebounds with a speed of 1.5 m/s.What is the magnitude of the impulse exerted on the ball by the floor?

Accepted Answer

A)  9.6 N  s
B)  2.4 N  s
C)  6.4 N  s
D)  1.6 N  s
E)  1.0 N  s

Question 9

An 8.0-kg object moving 4.0 m/s in the positive x direction has a one-dimensional collision with a 2.0-kg object moving 3.0 m/s in the opposite direction.The final velocity of the 8.0-kg object is 2.0 m/s in the positive x direction.What is the total kinetic energy of the two-mass system after the collision?

Accepted Answer

A)  32 J
B)  52 J
C)  41 J
D)  25 J
E)  29 J

Question 10

An astronaut outside a spaceship hammers a loose rivet back in place.What happens to the astronaut as he swings the hammer?

Accepted Answer

A)  Nothing.The spaceship takes up the momentum of the hammer.
B)  He moves away from the spaceship.
C)  He moves towards the spaceship.
D)  He moves towards the spaceship as he pulls the hammer back and moves away from it as he swings the hammer forward.
E)  He moves away from the spaceship as he pulls the hammer back and moves toward it as he swings the hammer forward.

Question 11

Two 0.20-kg balls,moving at 4 m/s east,strike a wall.Ball A bounces backwards at the same speed.Ball B stops.Which statement correctly describes the change in momentum of the two balls?

Accepted Answer

A)   B = Δ   A. 
E)  Δ   B > Δ   A. " class="answers-bank-image d-inline" rel="preload" > .
B)   B = Δ   A. 
E)  Δ   B > Δ   A. " class="answers-bank-image d-inline" rel="preload" > .
C)   B = Δ   A. 
E)  Δ   B > Δ   A. " class="answers-bank-image d-inline" rel="preload" > .
D)  Δ B = Δ   A. 
E)  Δ   B > Δ   A. " class="answers-bank-image d-inline" rel="preload" > B = Δ B = Δ   A. 
E)  Δ   B > Δ   A. " class="answers-bank-image d-inline" rel="preload" > A.
E)  Δ B = Δ   A. 
E)  Δ   B > Δ   A. " class="answers-bank-image d-inline" rel="preload" > B > Δ B = Δ   A. 
E)  Δ   B > Δ   A. " class="answers-bank-image d-inline" rel="preload" > A.

Question 12

A 5.0-g particle moving 60 m/s collides with a 2.0-g particle initially at rest.After the collision each of the particles has a velocity that is directed 30° from the original direction of motion of the 5.0-g particle.What is the speed of the 2.0-g particle after the collision?

Accepted Answer

A)  72 m/s
B)  87 m/s
C)  79 m/s
D)  94 m/s
E)  67 m/s

Question 13

A uniform thin wire has a length  
and is bent into a semicircular arc of radius R.If the wire starts at (x,y)= (R,0)and curves counterclockwise to (x,y)= (−R,0),what is the y coordinate of its center of mass?

Accepted Answer

The answer of A uniform thin wire has a length...

Question 14

A 1.5-kg playground ball is moving with a velocity of 3.0 m/s directed 30° below the horizontal just before it strikes a horizontal surface.The ball leaves this surface 0.50 s later with a velocity of 2.0 m/s directed 60° above the horizontal.What is the magnitude of the average resultant force on the ball?

Accepted Answer

A)  14 N
B)  11 N
C)  18 N
D)  22 N
E)  3.0 N

Question 15

A catapult fires an 800-kg rock with an initial velocity of 100 m/s at a 40° angle to the ground.The magnitude of the horizontal impulse the catapult receives from the rock is

Accepted Answer

A)  5.1 × 104 N 4 N   s. 
B)  6.1 × 104 N   s. 
C)  8.0 × 104 N   s. 
D)  5.0 × 105 N   s. 
E)  6.0 × 105 N   s. " class="answers-bank-image d-inline" rel="preload" > s.
B)  6.1 × 104 N 4 N   s. 
B)  6.1 × 104 N   s. 
C)  8.0 × 104 N   s. 
D)  5.0 × 105 N   s. 
E)  6.0 × 105 N   s. " class="answers-bank-image d-inline" rel="preload" > s.
C)  8.0 × 104 N 4 N   s. 
B)  6.1 × 104 N   s. 
C)  8.0 × 104 N   s. 
D)  5.0 × 105 N   s. 
E)  6.0 × 105 N   s. " class="answers-bank-image d-inline" rel="preload" > s.
D)  5.0 × 105 N 4 N   s. 
B)  6.1 × 104 N   s. 
C)  8.0 × 104 N   s. 
D)  5.0 × 105 N   s. 
E)  6.0 × 105 N   s. " class="answers-bank-image d-inline" rel="preload" > s.
E)  6.0 × 105 N 4 N   s. 
B)  6.1 × 104 N   s. 
C)  8.0 × 104 N   s. 
D)  5.0 × 105 N   s. 
E)  6.0 × 105 N   s. " class="answers-bank-image d-inline" rel="preload" > s.

Question 16

A rocket engine consumes 450 kg of fuel per minute.If the exhaust speed of the ejected fuel is 5.2 km/s,what is the thrust of the rocket?

Accepted Answer

A)  42 kN
B)  39 kN
C)  45 kN
D)  48 kN
E)  35 kN

Question 17

High-speed stroboscopic photographs show that the head of a golf club of mass 200 grams is traveling at 55.0 m/s just before it strikes a 46.0-gram golf ball at rest on a tee.After the collision,the clubhead travels (in the same direction)at 40.0 m/s.Find the speed of the golf ball just after impact.

Accepted Answer

The answer of High-speed stroboscopic photographs show that the head...

Question 18

A ball falls to the ground from height h and bounces to height h'.Momentum is conserved in the ball-earth system

Accepted Answer

A)  no matter what height h' it reaches.
B)  only if h' 
C)  only if h' = h.
D)  only if h' > h.
E)  only if h' ≥ h.

Question 19

A 3.0-kg mass is released from rest at point A of a circular frictionless track of radius 0.40 m as shown in the figure.The mass slides down the track and collides with a 1.4-kg mass that is initially at rest on a horizontal frictionless surface.If the masses stick together,what is their speed after the collision?

Accepted Answer

A)  2.1 m/s
B)  1.7 m/s
C)  1.9 m/s
D)  1.5 m/s
E)  2.3 m/s

Question 20

A 2.0-kg object moving 3.0 m/s strikes a 1.0-kg object initially at rest.Immediately after the collision,the 2.0-kg object has a velocity of 1.5 m/s directed 30° from its initial direction of motion.What is the x component of the velocity of the 1.0-kg object just after the collision?

Accepted Answer

A)  3.7 m/s
B)  3.4 m/s
C)  1.5 m/s
D)  2.4 m/s
E)  4.1 m/s

Exam 9: Linear Momentum and Collisions

The only force acting on a 2.0-kg object moving along the x axis is shown.If the velocity v_x is +2.0 m/s at t = 0,what is the velocity at t = 4.0 s?