Question

A boy stands at 78.4m from a building and throws a ball which just enters a window 39.2m above the ground. Calculate the velocity of projection of the ball.

Answer 1

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Answer 2

According to question

R = 2 × 78.4 m

H = 39.2 m

Relationship between R and H is

H = R Tanx / 4

Then,

Tanx = 4H / R

Tanx = (4 × 39.2) / (2 × 78.4)

Tanx = 1

x = 45°

Now,

H = u^2 Sin^2x / (2g)

u = sqrt(2gH) / Sinx

u = sqrt(2 × 9.8 × 39.2) / Sin45

u = sqrt(2 × 9.8 × 39.2) / (1/sqrt(2))

u = 39.2 m/s

Velocity of projection of ball is 39.2 m/s