Question

Question 6.6 Underline the correct alternative:

(a) When a conservative force does positive work on a body, the potential energy of the body increases/decreases/remains unaltered.

(b) Work done by a body against friction always results in a loss of its kinetic/potential energy.

(c) The rate of change of total momentum of a many-particle system is proportional to the external force/sum of the internal forces on the system.

(d) In an inelastic collision of two bodies, the quantities which do not change after the collision are the total kinetic energy/total linear momentum/total energy of the system of two bodies.

Chapter Work, Energy And Power Page 135

Answer 1

Hi____
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(a) Decreases
When we work on the body then i may be possible it become in motion so if we work on body ,then kinetic energy increase and potential energy decrease.
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(b) Kinetic energy
The work done against the direction of friction decrease the velocity of a body. so, there is a loss of kinetic energy of the body.
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(c) External force
If their is no internal force work on body then the external force is require to attend change in linear momentum .
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(d) Total linear momentum
The total linear momentum always remains conserved whether it is an elastic collision or an inelastic collision.
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hope it help

Answer 2

(a) when , a conservative force does positive work on a body , then potential energy of the body decreases .
because we know, negative potential gradient is known as Force .
e.g -dU/dx = F
dU/dx = - F here , it is clear that if F >0 then, dU < 0 { potential energy }
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(b) wordone by a body against friction always results in loss of its KINETIC ENERGY . due to friction body decrease the speed of it . so, decrease kinetic energy. hence , work done by a body against friction always results in a loss of its kinetic energy.
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(c) internal force can't change total momentum of a system of particles.also according to Law of conservation of linear momentum we know, if total EXTERNAL FORCE on the system is zero then , total linear momentum remains constant .
hence, the rate of change of total momentum of many particle system is proportional to the EXTERNAL force act on the system
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(d) in an inelastic collision , total linear momentum , and total energy of the system by two bodies do not change .
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