Question:
A small block B is placed on another block $A$ of mass $5 \mathrm{~kg}$ and length $20 \mathrm{~cm}$. Initially the block $B$ is near the right end of block $A$. A constant horizontal force of $10 \mathrm{~N}$ is applied to the block $A$. All the surfaces are assumed frictionless. Find the time elapsed before the block $B$ separates from $A$.
Solution:
$5 a=10$
$a=2 m / s^{2}$
$x-x_{0}=u t+\frac{1}{2} a t^{2}$
$20 \times 10^{-2}=\frac{2 \times t^{2}}{2}$
$(u=0)$
$t=\sqrt{0.2}=0.45 s$
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