Question

A 2 kg block is placed over a 4 kg block and both are placed on a smooth horizontal surface. The coefficient of friction between the blocks is 0.20. Find the acceleration of two blocks if a horizontal force of 12 N is applied to (a) the upper block , (b) the lower block. Take g=10 m/s².

Answer 1

(a). Force of the Friction = 2 × 10 × 0.2 = 4 N.

⇒ Force = 12 - 4

⇒ ma = 8

⇒ 2 × a = 8

∴ a =  4 m/s².

Now,

There will be no force on lower block., only force of friction will be there.

∴ ma = 4

⇒ a = 1 m/s².

(b). When Force will be applied in the lower block, then, there is no friction except the friction provided by the upper block, which is 4 N.

∴ 12 - 4 = 4a

⇒ a = 2 m/s².

Now,

For Upper block, only force of the Friction will be there,

4 = 2a

⇒ a = 2 m/s².

Hope it helps.