projectile motion

2010-09-05 7:31 pm

In a game of volleyball, a player is ready to serve. She stands at A, which is 3 m behind the baseline and serves the volleyball at a height of 2 m. The volleyball flies off with a velocity u at an angle of 30 degree to the horizontal. It just passes the net at C, at the height of 2.43 m. The baseline of the volleyball court is 9 m away from the net.

Find the magnitude of u ?

回答 (1)

天同

2010-09-05 9:44 pm

✔ 最佳答案

As there is no diagram given on the positions of A and C, I just make interpretation of them from the wording in the question.

Horizontal distance travelled by the volley ball before it flies off the net
= (9+3) m = 12 m
Time taken = 12/(u.cos(30))

Apply equation: s = U.t + (1/2).a.t^2 tot he vertical motion
with U =u.sin(30) = 0.5u, s = 2.43 m, a = -g(=-10 m/s2), t = 12/(u.cos(30))hence, 2.43 = (0.5u).[12/(u.cos(30))] + (1/2)/(-10).[12/(u.cos(30))]^2
solve for u gives u = 14.6 m/s

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