A steel ball of radius $2\, cm$ is at rest on a frictionless surface. Another ball of radius $4\,cm$ moving at a velocity of $81 \,cm/sec$ collides elastically with first ball. After collision the smaller ball moves with speed of ............. $\mathrm{cm} / \mathrm{sec}$
A steel ball of radius $2\, cm$ is at rest on a frictionless surface. Another ball of radius $4\,cm$ moving at a velocity of $81 \,cm/sec$ collides elastically with first ball. After collision the smaller ball moves with speed of ............. $\mathrm{cm} / \mathrm{sec}$
$81$
$63$
$144$
None of these
A steel ball of radius $2\, cm$ is at rest on a frictionless surface. Another ball of radius $4\,cm$ moving at a velocity of $81 \,cm/sec$ collides elastically with first ball. After collision the smaller ball moves with speed of ............. $\mathrm{cm} / \mathrm{sec}$
Ratio in radius of steel balls $= 1/2$
So, ratio in their masses$ = \frac{1}{8}$[As$M \propto V \propto {r^3}$]
Let ${m_1} = 8m$ and ${m_2} = m$
${v_2} = \frac{{2{m_1}{u_1}}}{{{m_1} + {m_2}}} = \frac{{2 \times 8m \times 81}}{{8m + m}} = 144\,cm/s$
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