Work, Power and Energy
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Question : 6
Total: 30
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/potentialenergy.
(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 collisionare the total kinetic energy/total linear momentum/total energy of the system of two bodies.
(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/potentialenergy.
(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 collisionare the total kinetic energy/total linear momentum/total energy of the system of two bodies.
Solution:
(a) Potential energy of the body decreases. The conservative force does positive work on a body, when it displaces the body in the direction of force. The body, therefore, approaches the centre of force, decreasing x. Hence, P.E. decreases.
(b) Workisdone by a body against friction at the expense of its kinetic energy. Hence K.E. of the body decreases.
(c) Internal forces cannot change the total or net momentum of a system. Hence the rate of change of total momentum of many particle system isproportional to the external force on the system.
(d) In an inelastic collision of two bodies, the quantities which do not change after the collision are total linear momentum and total energy of the system of two bodies. The total K.E. changes assome energy appears in other forms.
(b) Workisdone by a body against friction at the expense of its kinetic energy. Hence K.E. of the body decreases.
(c) Internal forces cannot change the total or net momentum of a system. Hence the rate of change of total momentum of many particle system isproportional to the external force on the system.
(d) In an inelastic collision of two bodies, the quantities which do not change after the collision are total linear momentum and total energy of the system of two bodies. The total K.E. changes assome energy appears in other forms.
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