A ball moving downward at velocity 30m/s strikes the floor,and bounces up at vel

Question

A ball moving downward at velocity 30m/s strikes the floor,and bounces up at velocity 18m/s, having been in contact with thefloor for 0.12 s. Find (a) the change in speed, (b) the change inthe velocity, (c) the average acceleration (magnitdude anddirection) during tthe impact, (d) the maximum height the balreaches after it leaves the floor. This is also one of the question i got early in my earlierexams and the professor did not show us how to do this problem. iwant to understand what i did wrong and not make the same mistakeon the midterm. A ball moving downward at velocity 30m/s strikes the floor,and bounces up at velocity 18m/s, having been in contact with thefloor for 0.12 s. Find (a) the change in speed, (b) the change inthe velocity, (c) the average acceleration (magnitdude anddirection) during tthe impact, (d) the maximum height the balreaches after it leaves the floor. This is also one of the question i got early in my earlierexams and the professor did not show us how to do this problem. iwant to understand what i did wrong and not make the same mistakeon the midterm.

Explanation / Answer

given the initial velocity is u = 30 m/s the initialspeed           =30 m/s the final velocity is v = - 18m/s                         as in the opposite direction the final speed is       = 18m/s inpact time t = 0.12s                     the changein the speed = 30 m/s - 18 m/s = 12 m/s          the change invelocity is V=( -18 m/s - 30 m/s ) = -48 m/s force F = change in momentum / time          ma = ( mV) / t             a = ( V ) / t = -400 m/s2 herenegetive indicate in the upward direction the maximum height reached by it is               H = v2 /2g = 16.53 m

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