2. A brother and sister are on a bridge which has a height of h 75m above the wa

Question

2. A brother and sister are on a bridge which has a height of h 75m above the water. The Her sister throws a ball straight down towards the water with a velocity of u, 25 brother throws the ball directly upwards with a velocity of u,-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? e) What is the velocity of the brothers ball just before it hits the water?

Explanation / Answer

here,

us = 25 m/s

ub = - 35 m/s

a)

the time taken by sister ball to hit the water be ts

h = us * ts + 0.5 * g * ts^2

75 = 25 * ts + 0.5 * 9.81 * ts^2

ts = 2.11 s

b)

let the time taken by the brother's ball to hit the water be tb

h = ub * tb + 0.5 * g * t^2

75 = - 35 * tb + 0.5 * 9.81 * tb^2

tb = 8.86 s

c)

the maximum height reached by the brother's ball , hmax = h + ub^2/2g

hmax = 75 + 35^2 /(2*9.8)

hmax = 137.5 m

d)

the final speed of sister's ball , vs = us + g * ts

vs = 25 + 9.8 * 2.11 m/s = 45.7 m/s

e)

the final speed of brother's ball , vb = ub + g * t

vb = - 35 + 9.8 * 8.86 m/s

vb = 51.8 m/s

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