Question

Select True or False for each statement.

1 Work cannot be done in the absence of motion.
2 Work is done when the form of energy changes.
3 Without friction or work by an external force, the sum of the potential and kinetic energies of a body is constant.
4 Energy conservation law for a projectile (no friction): Potential energy increase equals the kinetic energy decrease.
5. A source of energy is required to do work.
6. More power is required while slowly lifting a box than while lifting it up quickly.

Answer 1

1. True

Work done = F.d

if there is no motion then d (displacement ) will be zero so work done = 0

2. True ( work - enetgy relation)

3. False

work done by internal force can change its energy .

E.g - When bomb blasts in parts.

4. True.

from work - energ theorem.

work done by gravity = change in K.E.

increase in potential energy ( means negative work done by gravity ) = loss in K.E.

5. True

from work - energy theorem.

work done = change in energy

6. False

Power = work / time

same work done quickly, then time will be less .

ao powerr will be more.

power is less in slowly lifting.