Question

A boy is standing on top of a tower 175 m high tower which is 200 m away from 50 high building. He throws a ball horizontal to earth which lands on the top of the building. ( g = 10 ms -2 ) Find (a) Initial velocity of ball. (b) Time take by ball to land on building (c) Speed of ball by which it strike the building.

Answer 1

Answer:

The component of velocity in the vertical-upward direction is,

v=50sin(30

0

)=50×0.5=25m/s

Let the time taken to reach ground from initial position be t sec

The acceleration due to gravity is, g=10m/s

2

, in the vertical-downward direction.

and the distance traveled is, h=70m, in the vertical-downward direction.

So here, h=−vt+

2

1

gt

2

⟹70=−25t+(0.5×10×t

2

)

⟹t

2

−5t−14=0

Solving above quadratic equation, we get t=−2,7

As time is always positive, t=7s