Question

Normal forces and friction forces acting on bodies as they roll without slipping over a rough surface do work since there is a displacement

		True
		False

Internal forces do work because they always act in equal and opposite pairs

		True
		False

The elastic potential energy is always positive.

		True
		False

Answer 1

1) FALSE

Because for bodies as they roll without slipping there is no instantaneous displacement of the point in contant to ground surface.so the work done by the force on point is ZERO.

THEREFORE, the forces do no work due to zero displacement.

2) FALSE

INTERNAL FORCES DO NO WORK because as they always act in equal and opposite pairs the sum of work done is ZERO. hence there is no work done

3) FALSE

it it need not to be positive or negative.

Elastic potential energy is defined as the engergy that is stored by the work done to compress or strech the spring.

it is defined as the negetive of work done by the spring(compress or strech)

so, it may not be always positive