Q.1 How do you explain the fact that when a stone is dropped onto the ground, the change in the momentum of
the Earth is equal to that of the stone, while the change in the kinetic energy of the Earth is neglected ?
Q.2 You must have noticed that when you stir a cup of tea, the floating tea leaves collect at the centre of the
cup rather than at the outer rim. Can you explain this?
Q.3 Explain why you became physically tired when you push against a wall, fail to move it, and therefore do
not work on the wall.
Q.4 A man rowing a boat upstream is at rest with respect to the shore. (a) Is he doing any work? (b) If he
stops rowing and moves down with the stream, is any work being done on him?
Q.5 A man bounces on a trampoline, going a little higher with each bounce. Explain how he increases the total
mechanical energy.
Q.6 A rope tied to a body is pulled, causing the body to accelerate. But according to Newton's third law, the
body pulls back on the rope with an equal and opposite force. Is the total work done then zero? If so,
how can the body's kinetic energy change ? Explain.
Q.7 If there is a net force on a moving object that is nonzero and constant in magnitude, is it possible for the
total work done on the object to be zero? Explain, with an example that illustrates your answer.
Q.8 Consider yourself sitting in an elevator moving up with a constant velocity. In your reference frame, earth
has a large kinetic energy (
2
M
ev
2
1
). From where did it gain this kinetic energy?
Q.9 If you hang fuzzy dice from your rear-view mirror and drive through a banked curve, how can you tell
whether you are travelling less than, equal to, or greater than the speed used to calculate the banking
angle?
Q.10 If you observer a moving motorcycle moving with velocity v, you observe power expended by engine as
F.v
. But if you are observing the same motorcycle while moving with velocity u
, you will observe
power as F
(v u)
. Still petrol used by engine is same. Explain.
Q.11 A spirit level is tied to a string and whirled rapidly in a horizontal plane. Where will the bubble lie?
Q.12 A coin is put on the turntable of a record player. The motor is started, but before the final speed of
rotation is reached, the coin flies off. Explain.
Q.13 A loose bolt gets detached from the circumference of a big, rotating platform. In what direction will an
observer on the platform see it move? In what direction will an observer on the ground see it move?
Q.14 A small body slides along equally rough circular surfaces from A to B via route
1 and 2 of equal radius. In which case will the body's velocity be
greater?
Q.15 A man stretches a spring attached to the front wall of railway carriage over
a distance
l in a uniformly moving train. During this time the train covers a
distance L. Does the work done by the man depend on the coordinate
system related to the earth or the train? The man moves
opposite to the direction of motion of the train as he stretches the spring.
Q.16 Is there any net work done by external forces on a car moving with a constant speed along a straight
road?
Q.17 Is a body in circular motion in equilibrium?
Q.18 A wheel rotating at a constant angular velocity
about a fixed axis is in mechanical equilibrium because
no net external force or torque acts on it. However, the particles that make up the wheel undergo a
centripetal acceleration a
directed toward the axis. Since a
0
, how can the wheel be said to be in
equilibrium?
Q.19 A car speeds up while the engine delivers constant power. Is the acceleration greater at the beginning of
this process or at the end? Explain.
Q.20 A curve in a road has the banking angle calculated for 80 km/h. However, the road is covered with ice,
and you plan to creep around the highest lane at 20 km/h. What may happen to your car? Why?
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