You are helping your friend prepare for the next skateboard exhibition by determ

Question

You are helping your friend prepare for the next skateboard exhibition by determing if the planned program will work. Your friend will take a running start and then jump onto a stationary skateboard of weight Ws=15 lbs. The skateboard will glide in a straight line along a short, level section of track, then up a sloped concrete wall. The goal is to reach a height of at least 10 feet above the starting point before coming back down the slope. Your friend's maximum running speed to safely jump on the skateboard is v=20 ft/s . Your friend weighs Wp=150 lbs. What is the height hf that your friend will reach according to his plan?

Explanation / Answer

Here ,

let the speed of skate board after the friend jumps on it is v

Using conservation of momentum

(Ws + Wp) * v = Wp * vp

(15 + 150) * v = 20 * 150

v = 18.18 feet/s

Now , let the maximum height is h

Using third equation of motion

v^2 - u^2 - 2 * a * d

18.18^2 = 2 * 32.17 * h

h = 5.14 feet

the maximum height reached by friend is 5.14 feet

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