Question

A ball is thrown vertically upwards from the top of a tower with an initial velocity of 19.6 metre per second the world which is the ground after 5 seconds calculate the height of the tower the velocity of ball on reaching the ground take G is equal to 9.8 metre per second square ​

Answer 1

Given:

          Initial velocity of ball 'u' = 19.6 m/s

          Time taken by ball to reach ground 't' = 5 sec.

          Gravity 'g' = 9.8 m/s

Solution:

          we know that,

                                   ⇒ g =  

                                   ⇒   t =

                                          =

So,                               ⇒   t = 2 sec.

it means time taken to reach max. height is 2 seconds.

It means 2 seconds are taken by the ball to reach back to tower and rest of 1 second to reach to ground.

it means first two seconds are taken to make final velocity 'v' is zero (max. height).

                                   ⇒ v = 0 m/s

Time taken is 1 second to calculate height of tower (written above).

So, using equation of motion,

                                   ⇒

                                   ⇒ s = 19.6 x 1 + x 9.8 x

                                   ⇒ s = 24.5 m

From zero initial velocity at time 2 seconds to ground where time is 5 seconds. Now, time taken is 3 seconds from max. height to ground.

                                         

now,                             ⇒ v = u + at

                                    ⇒ v = 0 + 9.8 x 3

                                    ⇒ v = 29.4 m/s