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#	Question	Answer
1	What is the value of \(\hat{i} \cdot \hat{i}\)?	1.
2	Can work done by a force be negative?	Yes. When the force has a component opposite to the displacement (\(\theta > 90^\circ\)), the work done is negative.
3	What is the expression for the kinetic energy of a body of mass \( m \) moving with speed \( v \)?	\( K = \frac{1}{2} mv^2 \).
4	A weightlifter holds a 150 kg mass steadily on his shoulder for 30 s. How much work does he do on the load?	Zero, because the displacement is zero.
5	What is the principle of conservation of mechanical energy?	The total mechanical energy of a system is conserved if the forces doing work on it are conservative: \( K + V = \text{constant} \).
6	What is the change in potential energy equal to for a conservative force?	The negative of the work done by the force: \( \Delta V = -W \).
7	What is the maximum speed of a block of mass \( m \) attached to a spring of force constant \( k \) when released from a displacement \( x_m \)?	\( v_m = x_m \sqrt{\frac{k}{m}} \).
8	A car of mass 1000 kg moving at 18 km/h collides with a spring of constant \( 5.25 \times 10^3 \) N m⁻¹. What is the maximum compression of the spring (neglecting friction)?	2.00 m.
9	What is the dimensional formula of power?	\( [ML^2T^{-3}] \).
10	What happens in a one-dimensional elastic collision between two equal masses if one is initially at rest?	The first mass comes to rest and the second mass moves with the initial velocity of the first mass.
11	Is the zero of potential energy unique?	No. The zero of potential energy is arbitrary and can be chosen according to convenience.
12	What is the sign of the work done by friction on a body sliding down an inclined plane?	Negative.
13	A body starts from rest and undergoes one-dimensional motion with constant acceleration. The power delivered to it at time \( t \) is proportional to what?	\( t \).
14	A body of mass 0.5 kg travels with velocity \( v = 5 x^{3/2} \) m s⁻¹. What is the work done by the net force from \( x = 0 \) to \( x = 2 \) m?	50 J.
15	How much work does the cycle do on the road during the same skid?	Zero — though an equal 200 N reaction force acts on the road (Newton's third law), the road itself undergoes no displacement.
16	What is the block's final speed after crossing the rough patch?	1 m s⁻¹.
17	Since the mutual forces between two bodies are always equal and opposite (Newton's third law), must the work each does on the other always cancel?	No — \( W_{12} + W_{21} \) need not always be zero, though it may sometimes be true.
18	A rocket's casing burns up in flight due to friction with the atmosphere. At whose expense is this heat energy obtained — the rocket's or the atmosphere's?	The rocket's — friction decelerates the rocket, converting its own kinetic energy into heat.
19	An electron (KE = 10 keV) and a proton (KE = 100 keV) are detected in a cosmic ray experiment. Which is faster, and what is the ratio of their speeds?	The electron is much faster; \( v_e/v_p \approx 13.5 \), from \( v = \sqrt{2K/m} \) with \( m_e = 9.11\times10^{-31}\,\mathrm{kg} \), \( m_p = 1.67\times10^{-27}\,\mathrm{kg} \).
20	Bob A of a pendulum, released from 30° to the vertical, hits an identical bob B at rest on a table in an elastic collision. How high does bob A rise after the collision?	It does not rise at all — for an elastic collision between equal masses with one initially at rest, the first mass comes to rest (\( v_{1f}=0 \)), transferring all its velocity to the second.
21	For a windmill with A = 30 m², wind speed v = 36 km/h, air density 1.2 kg m⁻³, and 25% conversion efficiency, what electrical power does it produce?	4.5 kW — the wind's power is \( \frac{1}{2}\rho A v^3 = 18\,\mathrm{kW} \), of which 25% is converted.
22	(NEET 1995) If the momentum of a body is increased by 50%, by what percentage does its kinetic energy increase?	125% — since \( K \propto p^2 \), a 1.5× increase in momentum gives \( K_{\text{new}} = (1.5)^2 K_{\text{old}} = 2.25\,K_{\text{old}} \).