2. A brother and sister are on a bridge which has a height of h 75m above the wa
ID: 1657936 • Letter: 2
Question
2. A brother and sister are on a bridge which has a height of h 75m above the water. The sister throws a ball straight down towards the water with a velocity of u, = 25 . Her brother throws the ball directly upwards with a velocity of vi 35. a) How long does it take the sisters ball to hit the water? b) How long does it take the brothers ball to hit the water? c) What is the maximum height above the water that the brothers ball reaches? d) What is the velocity of the sisters ball just before it hits the water? o) What is the velocity of the brothers ball just before it hits the water?Explanation / Answer
(A) yf- yi = v0 t + a t^2 /2
0 - 75 = -25t - 9.8 t^2 /2
4.9 t^2 + 25t - 75 = 0
t = 2.12 sec
(B) 0 - 75 = 35t - 9.8 t^2 /2
4.9 t^2 - 35t - 75 = 0
t = 8.87 sec
(C) vf^2 - v0^2 = 2 a d
for d_max , vf = 0
0^2 - 35^2 = 2(-9.8)(Hmax)
Hmax = 62.5 m
(d) vf = vo + a t
v = -25 - 9.8(2.12) = - 45.8 m/s
velocity is 45.8 m/s downward
(e) v = 35 - (9.8 x 8.87)
v = - 51.9 m/s
velocity is 51.9 m/s downwards.
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