Question

Need answer asap pls

Answer 1

velocity of the ball thrown by the boy relative to himself is $20 m/s.$

Answer 2

We have to find the velocity of the ball thrown by the boy relative to himself.

For this first we have to find the angle at which ball has thrown.

Suppose  the angle at which ball is thrown, is α.

velocity of the boy with respect to ground is 'u' and velocity of ball with respect to boy is 'v'.

component of velocity of ball along plane = u + vcosα

component of velocity of ball perpendicular to plane = vsinα

As a  boy can throw the ball only when distance covered by the boy and the distance covered by the ball along plane are same.

hence distance covered by the boy = distance covered by the ball

 ut + 1/2gsin37°t² = (u + vcosα)t + 1/2gsin37°t²

∴ cosα = 0 = cos90°

∴ α = 90°

so the ball is thrown vertically upwards, isn't it ?

we also know that the net displacement of ball with respect to plane is zero because the the same position in vertical direction.

so,  

 0 = (vsin90°)t + 1/2(-gcos37°)t²

 v = gcos37°t/2

using cos37° = 4/5 , t = 5sec and g = 10m/s²

so, v = (10 × 4/5 × 5)/2 = 20m/s

therefore the velocity of the ball thrown by the boy relative to himself is 20 m/s.

Hence option second is correct.