1. Suppose you are standing on an ice skating rink. There is negligible friction

Question

1. Suppose you are standing on an ice skating rink. There is negligible friction between your feet and the ice, A friend throws you a 0.400 kg ball that is traveling horizontally at 10.0 m/s. Your mass is 70.0 kg. Answer (a) and (b) below, showing governing equations and all work leading to correct answer for credit.. (2 points) (a) If you catch the ball, with what speed do you and the ball move afterward? State your results to three significant figures. (2 points) (b) Suppose the ball just hits you and bounces off your chest, so that afterward it is moving at 8.00 m/s in the opposite direction. What is your speed in this case? State results with three significant figures. Conservation of Mechanical Energy and Momentum in Skiing Suppose a man with a mass of 65 kg skis down a frictionless hill that is 5.0 m high. At bottom of hill the terrain levels out. As the man reaches the horizontal section, he grabs a 20-kg backpack and skis off a 2.0 m high ledge in parabolic trajectory motion. Answer questions 2,3, 4 and 5 below. Show all governing equations and correct work neatly credit. State results with two significant figures. (2 points) 2. What is speed of the skier just before he grabs the backpack? It is a good practice to use subscripts to distinguish mass of skier and mass backpack. 8

Explanation / Answer

1. (A) Applying momentum conservation,

pi = pf

(0.400 x 10) + (70 x 0) = (70 + 0.40) v

v = 0.0568 m/s

(B) (0.40 x 10) + (70 x 0) = (70 x v) + (0.40 x -8)

v = 0.103 m/s

2. Applying energy conservation,

PEi + KEi = PEf + KEf

m g (5) + 0 = 0 + m v^2 /2

v = 9.90 m/s

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