Question

# 3) A ball is thrown leftward from the left edge of a roof at height “h”...

3) A ball is thrown leftward from the left edge of a roof at height “h” above the ground. The ball hits the ground 1.5 sec later at a distance d = 25 m from the building and at an angle θ = 60° with the horizontal.

a) What is the value of “h”?

b) What is the magnitude of the initial velocity?

c) What is the angle of the initial velocity?

horizontal velocity

Vx = 25 / 1.5 =16.667 m/s

net velocity just before impact

Vx = V cos 60

16.667 = V cos 60

V = 33.33 m/s

vertical component of velocity

vy = V sin 60 = 28.867 m/s

using 1st equation of motion

vy = uy + gt

uy = 28.867 - 9.8* 1.5

uy = 14.167 m/s

ux = vx = 16.667 m/s

net velocity of projection

u^2 = ux^2 + uy^2

u = 21.874 m/s ====>>>> Ans (b)

direction

x = arctan ( uy/ux) = 40.36 ===>>> Ans (c)

using 3 rd equation of motion

v^2 = u^2 + 2 g h

h = 32.266 m===>>> Ans (a)

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