Question

Example: 29
A man is standing on the top of a building, throws a ball with speed 5m/s from 30 m height above
ground level. How much time it takes to reach the ground,
CHADDHA CLASSES, JALOMON
amnle. 30
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Answer 1

Explanation:

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Answer 2

The time taken is 3 seconds.

GIVEN

A man is standing on the top of a building, throws a ball with speed 5m/s from 30 m height above

ground level.

TO FIND

How much time it takes to reach the ground?

SOLUTION

We can simply solve the above problem as follows;

It is given,

Initial velocity of the ball = 5m/s

Final velocity of the ball = 0

Height of the building = 30 meters

Applying second equation of motion;

s = ut + (1/2)at²

Where,

s = Height of the tower

u = initial velocity

a = acceleration due to gravity

t = time taken

Putting the values in the above formula we get;

30 = 5t + (1/2)× 10 × t²

30 = 5t + 5t²

Dividing the whole equation by 5

6 = t + t²

Rearranging the terms

t² + t - 6 = 0

Simplifying the above equation;

t² + 3t - 2t - 6 = 0

t (t + 3) -2(t + 3) = 0

t-2 = 0

t = 2 sec

t +3 = 0

t = -3 sec

Since time cannot be negative.

Hence, The time taken is 3 seconds.

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