A ball is thrown down vertically with an initial speed of 25 ft/s from a height

Question

A ball is thrown down vertically with an initialspeed of 25 ft/s from a height of 30 ft. (a) What is itsspeed (in ft/s) just before it strikes the ground? (b) How longdoes the ball take to reach the ground? What would be the answersto (c) part a and (d) part b if the ball were thrownupward from the same height and with the same initialspeed ? Before solving any equations, decide whether the answers to(c) and (d) should be greater than, less than, or the same as in(a) and (b).

Explanation / Answer

initial speed of 25 ft/s height of 30 ft/s conservation of energy m*g*30ft +m*(25)2/2=m*x2/2 ; g=32ft/s2 => speed (in ft/s) just before it strikes the ground :x=50.45 ft/s the time needed: t=(x-25)/32=0.795 s for part c & d, the same speed to a , becausewhen it fall back to thrown point..the stage will be the same. but we get the difference in time, of course, will be morelonger. the time needed for the ball felt back to the thrown point:t'=2*25ft/g=1.5625 s t =0.795 +2*25ft/g=2.36 s for partd

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