CBSE Class 11-science Answered

The ball is thrown with velocity u = 30 m/s at an angle 30^o when the platform velocity is v = 3 m/s .

Hence intial vertical component of velocity of ball is ( u sin30 + v ) = 18 m/s

Let the ball hit the platform when it reaches the height h from the position when the ball is thrown

as shown in figure.

Vertical displacement for the ball is

h = 18 t - [ (1/2) × g t²  ]  =  18 t - 4.9 t² ......................... (1)

where g = 9.8 m/s² is acceleration due to gravity  and t is time taken.

Platfrom is moving with acceleration a = 5 m/s² .  Hence vertical displacement for platform is

h = 3 t + [ (1/2) a t² ] = 3t + 2.5 t²  ..................................(2)

Time taken t for the ball to hit the platform is calculated by equating eqn.(1) and (2)

3t + 2.5 t² = 18 t - 4.9 t²

From above expression , we get t ≈ 2 s