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?
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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
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