Question

A lizard, at an initial distance of $21$ cm behind an insect, moves from rest with an
acceleration of $2cm/s^2$ and pursues the insect which is crawling uniformly along a
straight line at a speed of $20$ cm/s. Then the lizard will catch the insect after

• A. $20$ s
• B. $1$ s
• C. $21$ s
• D. $24$ s

Answer 1

Answer: (C)

$21$ s

Let t be the time in which the lizard will catch the insect.

Distance traveled by lizard $=$ 21 + distance traveled by insect.

$ut+\frac{1}{2}a{t}^2=21+vt$

$0+\frac{1}{2}2t^2=21+20t$

$t^2-20t-21=0$

solving this $t=21,-1$

t cannot be -ve.

$t=21sec.$