1. A3-kg ball has a velocity of 2 m/s to the left just before it strikes a wall

Question

1. A3-kg ball has a velocity of 2 m/s to the left just before it strikes a wall ahl 0 back with a velocity of 2 m/s to the right. What is the impulse on the ball? (a) 0 kg.m/s (b) 6 kg.m/s to the right (c) 6 kg.m/s to the left (d) 12 kg m/s to the right (e) 12 kg m/s to the left 2. A 0.20-kg puck at the end of a 0.70-m long string is being spun in a horizontal circle on a frictionless table at a speed of 3.4 m/s. What is the tension in the string? (a) 32.3 N (b) 4.72 N (c) 3.30 N (d) 0.97 N 3. A 100-kg person and a 50-kg person are at rest together on a frictionless surface. If the lighter person pushes off with a speed of 4 m/s, what will be the speed of the heavier person? (a) 8 m/s (b) 4 m/s (c) 2 m/s (d) Not enough information 4. A child drops a baseball from a treehouse. The ball is at rest just before the child drops it, and it comes to a stop when it hits the ground. What work was done on the ball by its weight? (a) Positive work (b) Zero work (c) Negative work (d) It depends on which direction we define as positive.

Explanation / Answer

1. vi = - 2 m/s and vf = 2 m/s

impulse = change in momentum

= m (vf - vi)

= 3(2 - (-2))

= 12 kg m/s to the right

Ans(d)

2. T = m a_c = m v^2 / r

T = 0.20 x 3.4^2 / 0.70

T = 3.30 N
Ans(C)

3. applying momentum conservation,

pi = pf

0 = (50 x 4) - (100 v)

v = 2 m/s

Ans(c)

4. weight is downward and displacement is also downward.

so work done will be positive .

Ans(a)

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