KVPY SX SB Exam 2013 Question Paper

Question : 92 of 120

Marks: +1, -0

A small boy is throwing a ball towards a wall 6 m in front of him. He releases the ball at a height of 1.4 m from the ground. The ball bounces from the wall at a height of 3 m, rebounds from the ground and reaches the boy’s hand exactly at the point of release. Assuming the two bounces (one from the wall and the other from the ground) to be perfectly elastic, how far ahead o f the boy did the ball bounce from the ground?

1.5 m
2.5 m
3.5 m
4.5 m

Validate

Solution:

3=(6+x)\tan θ[1-{6+x}/12]

3={(6+x)(6-x)\tan θ}/12

1.4=x\tan θ[1=x/12]

1.4={x(12-x)}/12\tan θ

30/14={36-x^2}/{12x-x^2}

360x - 30x^2 = 36 ×14 -14x^2

16x^2 - 360x + 36 ×14=0

x={360±√{(360)^2-4×36×14×16}}/32

x={360±312}/32=48/32=1.5

Go to Question:

Prev Question

Next Question