Question

A person pushes a block of mass 0.25kg along a horizontal table with a force of magnitude 5 N for a distance of 0.5 m. The fictional force between block and table is 1 N .The average power of pushing force is?

Answer 1

Solution :-

As per the given data ,

• Mass of the block(m) = 0.25 kg
• Force applied (F)= 5N
• Displacement (s)= 0.5 m
• Frictional force (f ) = - 1 N

Step I : Net force acting on the block

➜ Fnet = F + f

➜ F net = 5 - 1

➜ Fnet = 4 N

Step II : Acceleration of the block

As per Newton's law of motion ,

➜ Fnet = ma

➜ 4 = 0.25 x a

➜ a = 400 / 25

➜ a = 16 m / s²

Step III :- time taken by the block

By applying second equation of motion ,

➜ s = ut + at² / 2

➜ s = at² / 2

➜ t = √ 2 x 0.5 /16

➜ t = √ 1 / 16

➜ t = 1 / 4

➜ t = 0.25 s

Step IV : Work done

We know that ,

➜ W = F . s

➜ W = 4 x 0.5

➜ W = 2 J

Step V : Average power

we know that ,

➜ P = W / t

➜ P = 2 / 0.25

➜ P = 200 / 25

➜ P = 8 W

The average power of pushing force is 8 W