Question

A motor cyclist is trying to jump across a path as shown by driving horizontally off a cliff A at a speed of 5 ms^-1. [Ignore air resistance and take g = 10 ms^-2]. The speed with which he touches the peak B is

(a) 2.0 ms^-1

(b) 12 ms^-1

(c) 25 ms^-1

(d) 15 ms^-1

Answer 1

The correct option is (d) 15 ms^-1

Explanation:

Speed in horizontal direction remains constant during whole journey because there is no acceleration in this direction.

As,  v_h = 5 ms^-1

In vertical direction 

Loss of gravitational potential energy = Gain in KE

mgh = 1/2 mv²_v

v²_v = 2gh

= 2 x 10 x (70 -60) = 200 ms^-1

Hence, the speed with which he touches the cliff B is