Question 11:
easyAssertion (A): Work done by or against force of friction in moving a body in any round trip is always zero.
Reason (R): Frictional force is a conservative force.
Frictional force is a non-conservative force. Work done by a non-conservative force over a closed path is generally not zero. Therefore, both Assertion and Reason are false.
Question 12:
easyAssertion (A): No work is done when an electron completes a circular or an elliptical orbit around the stationary nucleus of an atom.
Reason (R): Electrostatic force is a conservative force.
Electrostatic force is a conservative force. For any conservative force, the work done on a particle moving along a closed path is zero. Therefore, both Assertion and Reason are true, and Reason is the correct explanation of the Assertion.
Question 13:
easyAssertion (A): If a spring is compressed, energy is stored in spring and when it is elongated, energy is released.
Reason (R): Work done by spring force is equal to change in potential energy of the spring.
Elastic potential energy `\(U = \frac{1}{2} k x^2\)` is stored in a spring when it is compressed or elongated. Energy is released when the spring moves towards its equilibrium position, not during elongation itself. Thus, assertion (A) is false. For a conservative force like spring force, `\(W = -\Delta U\)`, so work done by spring force is equal to the negative of the change in potential energy.
Thus, reason (R) is also false. Both assertion and reason are false.
Question 14:
easyAssertion (A): Frictional forces are conservative forces.
Reason (R): Potential energy can be associated with frictional forces.
Frictional forces are non-conservative forces because the work done by them depends on the path taken and energy is dissipated as heat. Potential energy can only be associated with conservative forces (e.g., gravitational, elastic).
Therefore, both assertion and reason are false.