Sum

A small block B is placed on another block A of mass 5 kg and length 20 cm. Initially, the block B is near the right end of block A (In the following Figure). A constant horizontal force of 10 N is applied to the block A. All the surfaces are assumed frictionless. Find the time that elapses before block B separates from A.

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#### Solution

Mass of block A, m = 5 kg

F = ma = 10 N

\[\Rightarrow a = \frac{10}{5} = 2 m/ s^2\]

As there is no friction between A and B, when block A moves, block B remains at rest in its position.

Initial velocity of A, u = 0

Distance covered by A to separate out,

s = 0.2 m

Using \[s = ut + \frac{1}{2}a t^2\]

\[0 . 2 = 0 + \frac{1}{2} \times 2 t^2\]

⇒ t^{2} = 0.2

⇒ t = 0.44 s ≈ 0.45 s

Concept: Newton’s Second Law of Motion

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