Answer : Question 32 ( Interference)
a) Alternating loud and soft sound
b) * coherent source provides – constant phase difference when the two waves
interfere
*the same kind of interference, whether constructive/destructive interference will
occur at the same place all the time
*therefore the interference pattern of alternating loud and soft sound can be heard
c) ax = λD
λ = ax/D
= 0.6 x 2.4 / 3
= 0.48 m
Answer : Question 27
a) i) optical fibre is denser than air, ray is refracted towards normal
ii) Total internal reflection(T.I.R) occur , where angle of critical more than critical angle
b) draw a ray going away 
from normal at B
Answer : Question 16( Archimedes Principle)
a) i. The block rises to the surface of water
ii. The block rises to the surface of water because the upthrus(buoyant force)t on the block is greater than the weight of the block
b) The block rises to the surface of water.
c) i. Volume of the block = m/p
= 0.18/900
= 0.0002 m³
Upthrust = pvg
= 0.0002 x 1200 x 10
= 2.4 N
Use Principle of Equilibrium of Forces to answer this part(Total Force Top = Total Force Down)
Weight of load + Weight of block = Upthrust
So, Weight of load = Upthrust - Weight of block [ w=mg…so w= 0.18 x 10 = 1.8]
= 2.4 – ( 1.8)
= 0.6 N
ii. The block will immerse deeper in the liquid.
Question 10
a) i) Both the coin and feather fall due to the gravitational pull. In the lab, when they move through the air, the air resists against their motion. The air resistance depends on the shape of the body and velocity of the body. The feather has greater surface area than the coin. Hence the feather experiences greater air resistance and its acceleration decreases.
There is no air in the vacuum cylinder. Thus two objects move down without air
resistance and reach the bottom of the cylinder at the same time.
ii) Parachute-----payung terjun
b) i) arrange data :
m1 = 200kg, u=12m/s
m2 = 300kg, v= ?? ( tak tahu)
this is an …..inelastic collision…
m1u1 x m2u2 = (m1+m2)v………hey u2=0 since its not moving
200 x 12 = (200+3000)v
v = 0.75 m/s
ii) Loss of K.E = Work done against friction
Loss of K.E = ½ mv2 = ½ x 3200 x 0.75² = 900 J .....all the K.E used to move the stomp
Work done = force(friction) x distance
900 = f x 0.2 …………..must change cm to m
f = 4500 N
Answer : Question 6
a) i) Momentum is the product of mass and velocity of the object
ii) The plasticine ball is flatter on wood than the plasticine on the sponge
There is no change on the surface of the wood but the surface of the sponge is dented by the palsticine ball. The time of impact on hard wood is shorter that that on the sponge. Hence the impulsive force on the wood is greater than on the sponge since impulsive force is the rate of change of momentum.
b) Before the plasticine ball is released from a height, it possesses G.P.E(gravitational potential energy). According to the principle of conservation of energy, when it is released, G.P.E is converted to K.E(kinetic energy). When it hits the wood or sponge, the K.E changes to sound energy and heat energy due to frictional force between the ball and the surface.
c) i)1. Satellite is made of materials with high melting point so that it is not easily melted when it reaches a high temperature
2. Satellite is designed to have an aerofoil shape which gradually tapers towards the end to decrease the air resistance.
3. Satellite is sheltered (protected) with insulators to prevent heat from entering.
ii) 1. Satellite is made of materials of low density to reduce the impulsive force on landing.
2. Satellite is made of composite material which is light, hard and strong so that it is not easily broken up on landing.-----you can use this answer for other questions as well
3. Satellite is attached with a parachute so that is descends slowly and decrease its velocity on landing.
