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AL-Essay-Revision / p.1
1.
(88-IIA-5a)
(a)
Compare the appropriate physical conservation laws which apply to
(i)
elastic and
(ii)
non-elastic
collisions between a moving non-rotating body and a stationary body.
(3 marks)
2.
(92-IIA-1a,b)
(a) Explain the meanings of Newton’s second and third Laws of Motion.
(3 marks)
(b) Apply these laws to the rapid impact between two bodies, which were initially moving
with unequal velocities along the same direction, and show that linear momentum is
conserved. Explain whether the total kinetic energy is necessarily conserved, or not.
(7 marks)
3.
(95-IIB-1a)
(a)
In each of the following situations, use Newton’s laws of motion to explain whether
or not a net force is acting on the body. If no net force is acting, describe how the
forces are balanced. If a net force is acting, explain the origin of the net force and
state its direction.
(i)
A raindrop which falls at terminal speed.
(ii)
A ping pong ball which collides obliquely with a smooth wall.
(iii) A communications satellite which maintains a constant position above the
earth’s surface.
(8 marks)
4.
(97-IIB-1a)
(a)
A man pushes a heavy rock resting on the ground, but it does not move. A student
says that this is because the pushing force is balanced by the reaction of this force.
Comment, with the aid of a diagram, on whether the student’s argument is correct.
(2 marks)
5.
(99-IIB-1b)
(b)
With the apparatus available in a school laboratory, describe a simple experiment to
investigate the dependence of the stopping distance of a vehicle on is initial kinetic
energy under the action of a constant resistive force. State and describe how to verify
the expected result. State the source(s) of error.
(4 marks)
6.
(00-IIB-1)
(a)
Explain briefly whether the linear momentum of each of the following underlined
objects is conserved :
(i)
A billiard ball strikes the smooth cushion of a billiard table at an angle and
rebounds with the same speed.
(ii)
A rocket rises vertically upward during launching in the atmosphere near the
earth’s surface.
(iii) A radioactive nucleus emits an -particle.
(3 marks)
(b) A ball of mass m1 moving with velocity u1 undergoes head-on collision with another
ball of mass m2 which is initially at rest on a smooth horizontal surface. The collision
is perfectly elastic.
AL-Essay-Revision / p.2
(i)
What is meant by a perfectly elastic collision? Show that the velocity of the
ball of mass m1 after collision is given by
 m1  m 2 

u1
 m1  m 2 
(ii)
Use the result in (i) to describe examples of collision where
(I)
m1 is much greater than m2;
(II)
m1 equals m2; and
(III) m1 is much smaller than m2 .
Hence explain the implication for the choice of materials used as moderators for
neutrons in a nuclear reactor.
(7 marks)
(c) The diagram shows a set-up used to measure the speed of a bullet in the laboratory.
The bullet (of mass m, in the form of a small metal ball) is ‘fired’ horizontally towards
a block of wood (of mass M, in which a hole has been drilled) suspended from two
vertical inextensible strings (each of length L). On striking the block, the bullet is
embedded and the block rises by swinging through an angle  as shown.
(i)
Suggest a simple method to ‘fire’ the bullet in laboratory. How can we ensure
that the bullet will be embedded in the block without rebound?
(ii)
7.
Show that the speed of the bullet is given by the relation
m M 
v
 2 gL(1  cos  ) where g is the acceleration due to gravity.
 m 
Indicate clearly the conservation laws applied in deriving the relation. Discuss
and account for the discrepancy between the experimental and theoretical
values of v. (Neglect the effects of air resistance.)
(6 marks)
(01-IIB-1)
(a)
(i)
(ii)
(b)
(i)
What is meant by inertia ? Briefly explain its relation to force.
Use an example to illustrate that an object may not necessarily be at rest
when the net force acting on it is zero.
(3 marks)
Give an example in which a body is accelerating but its speed remains
unchanged. Briefly explain the motion by using the concepts of force and the
change of momentum.
AL-Essay-Revision / p.3
(ii)
8.
Briefly outline an experiment to show the following relation:
Force  mass  acceleration
Under what condition(s) would the relation become an equation?
(8 marks)
(c)
By considering a head-on collision between two moving spheres of different masses,
show clearly that the principle of conservation of momentum follows from Newton’s
laws of motion.
(5 marks)
(02-IIB-1b,c)
(b)
(i)
A boy starts to jump vertically from a horizontal ground. Identify all action
and reaction pairs involved. Account for his initial acceleration.
(ii)
Use the concept of action and reaction to explain the launching of rockets.
(c)
9.
Consider the head-on collision of an a particle with an isolated gold nucleus that is
stationary initially. Explain whether or not the linear momentum of he system is
conserved. Describe the energy change during the collision process. (Assume that no
excitation of the gold nucleus occurs.)
(03-IIB-1a,b)
(a)
(i)
A block moving with a certain initial speed is acted upon by a constant
resultant force F along its direction of motion. Show that the work done by F
is equal to the change in kinetic energy of the block.
(ii)
An electron is projected with an initial velocity v into a region with a
uniform magnetic field perpendicular to v. Discuss the work done by the
magnetic force acting on the electron and its change in kinetic energy.
(Neglect the effects of gravity.)
(b)
An object is thrown vertically upward from the earth 's surface with a certain initial
speed. It rises to a maximum height and then falls back to the starting point.
(i)
What is the work done by the gravitational force in the process? Explain.
(ii)
Discuss the effect(s), if any, of the air resistance and upthrust on the final
speed of the object when it returns to the starting point. Referring to this
example, explain the principle of conservation of mechanical energy and
state the necessary condition for it to be valid. (Note: when an object is
immersed in a fluid, a constant upward force or upthrust acts on it by the
fluid.)