Question

A horizontal force of 25N necessary to just hold a block stationary against a wall the coefficient of friction between the block and wall is 0.4 the weight of the block is

Answer 1

Solution :

⏭ Given:

✏ A horizontal force of 25N necessary to just hold a block stationary against a wall.

✏ Co-efficient of friction between the block and wall is 0.4

⏭ To Find:

✏ Weight of block

⏭ Diagram:

✏ Please, see the attachment for better understanding.

⏭ Calculation:

✏ Let F be the force applied on the block. N is normal reaction of the wall on the block. W is weight of block acting vertically downward. f is the force of friction between the wall and the block which acts upwards as shown in the attachment.

✏ The block will not fall, if

$\mapsto \sf \: \underline{\red{Frictional \: Force = Weight \: Force}} \\ \\ \therefore \: \boxed{ \sf{f = \mu \times {N} = W} }\\ \\ \mapsto \sf \: \underline{ \blue{External \: Force = Normal \: Reaction}} \\ \\ \therefore \: \boxed{ \sf{F{ \tiny{ext}} = N}} \\ \\ \implies \sf \: \mu \times {F{ \tiny{ext}}} = W \\ \\ \implies \sf \: W = 25 \times 0.4 \\ \\ \implies \: \underline{ \boxed{ \bold{ \sf{ \purple{ \large{Weight = 10 \: N}}}}}} \: \gray{ \bigstar}$