# A block of mass 10kg is dropped from top of a cliff 100m high at same time a bullet of mass 10g is fired vertically upward with velocity of 100m/s. after how much time will they meet ?

$(a)\;10s \quad (b)\;0.5s \quad (c)\;7s \quad (d)\;1s$

Let they meet after t second
If block travels 's'm distance then in same time the bullet travells(100-s)m
For block
$s=0 \times t +\large\frac{1}{2}$$\times 10 \times t^2 For bullet 100-s=100 \times t +\large\frac{1}{2}$$(-10) \times t^2$
Solving this we get $t=1 second$
Hence d is the correct answer.

edited Jul 24, 2014