Question

24. A steel ball of radius 2 cm is at rest on a frictionless surface. Another ball of radius 4cm
moving at a velocity of 81 cm/sec collides elastically with first ball. After collision the
smaller ball moves with speed of
(a) 81 cm/sec (b) 63 cm/sec (c) 144 cm/sec
(d) None of these​

Answer 1

Answer:

Ratio in radius of steel balls =1/2

Mass= Density x Volume

V∝r ^3⟹M∝r ^3

So, ratio in their masses =

$\frac{1}{8}$

Let m 1 =8m and m 2 =m

Applying momentum consercation:

$v2 = frac{2m1u1 }{m1 + m2}$

$= \frac{ ( 2 \times 8m \times 81)}{8m + m}$

=144cm/s