A crate is pushed horizontally with 100N across a 5m floor. If the frictional force between the crate and the floor is 40N, then the kinetic energy gained by the crate is . 200j 240j 250j 300j 500j

Ameena Grade: 12th pass

        A crate is pushed horizontally with 100N across a 5m floor. If the frictional force between the crate and the floor is 40N, then the kinetic energy gained by the crate is .
	200j
	240j
	250j
	300j
	500j

one year ago

Answers : (1)

Samyak Jain

333 Points

							Contant horizontal force of magnitude F = 100 N is acting on the crate. It displaces the crate by s = 5 m.
Thus, work done by this force is F.s = F.s = 100 . 5 = 500 J.
 the direction of force is same as that of displacement.
Frictional force between crate and floor is f = 40 N. It is too acting for the displaceement s = 5 m.
Its work done is f.s = – f.s = – 40 . 5 = – 200 J.
 the direction of force is opposite to that of displacement.
Total work done by the forces acting on the crate is 500 J + (– 200 J) = 300 J.
As we know that net work done by all the forces acting on a body is equal to change in its kinetic energy,
300 J = KE = KE_f – KE_i . Assuming the crate to be at rest initially, KE_i = 0.
 KE_f = 300 J .