57. The average acceleration during contact with the floor is aavg= (v2– v1) / Δt, where v1is its velocity just before striking the floor, v2is its velocity just as it leaves the floor, and Δtis the duration of contact with the floor (12 ×10–3s). (a) Taking the yaxis to be positively upward and placing the origin at the point where the ball is dropped, we first find the velocity just before striking the floor, using 22102vvgy=−. With v0= 0 and y= – 4.00 m, the result is 2122(9.8 m/s )( 4.00 m)8.85 m/svgy=− −−where the negative root is chosen because the ball is traveling downward. To find the velocity just after hitting the floor (as it ascends without air friction to a height of 2.00 m),
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