Please show all work!!! I got (a) but don\'t know how to do (b). Thank you!!! 43

Question

Please show all work!!! I got (a) but don't know how to do (b). Thank you!!!

43P. A 2000-kg railroad flatcar, which can move on the tracks with virtually no friction, is sitting motionless next to a station platform. A 100-kg football player is running along the platform parallel to the tracks at 10 m/s. He jumps on to the back of the flatcar. (a) What is the speed of the flatcar after he is aboard and at rest on the flatcar? (b) Now he starts to walk. at 0.5 m/s relative to the flatcar, to the front on the car. What is the speed of the flatcar as he walks?

Explanation / Answer

a) using momentum conservation,

initial = final moemntum

2000 x 0 + 100 x10 = (2000 + 100)v

v = 0.476 m/s

b) as player moves with 0.5 m/s wrt to car. suppose that time speed of car is v.

so speed of player wrt ground = v + 0.5
using momentum conservation again,

(2000 + 100)0.476 = (100 x (v + 0.5)) + (2000 x v)

v = 0.463 m/s

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