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Physics Form 4 Answers

c = 500 × 120 Explanation: Shiny materials 2d = v × t
0.5 × 72 can prevent heat loss through = 340 × 2.0
–1
–1
= 1 667 J kg °C radiation. = 680 m
(b) (i) degree of hotness • Suggestion: The covered cup Therefore,
(ii) Volume of gas decreases. can be stored in a pocket h = 340 m
(iii) Absolute zero temperature made of bamboo cloth. Q2 (a) v = 1500 m s , t = 0.12 s
–1
(0 K or – 273°C) Explanation: So that there is Distance travelled by the pulse
(iv) The freezing gas molecules a layer of air trapped inside it = v × t = 1500 × 0.12 = 180 m
do not move. can reduce heat loss. (b) Distance of the shoal of fish
Section B below the boat = 180 = 90 m
2. (a) Heat is a form of energy that 2
can flow from area of high Chapter (c) Ultrasonic waves can transfer more
temperatures to area of low 5 energy than audible sound
temperatures. Waves waves.
(b) (i) • The mass of water in
kettle P is smaller than Checkpoint 5.1 Checkpoint 5.4
the mass of water in
kettle Q. Q1 (a) A wave is a travelling Q1 (a)
• The heat energy supplied disturbance from a vibrating or
to the kettle P and the oscillating source.
kettle Q are the same. (b) Transverse waves
• The temperature of water (c)
rise in kettle P is higher
than the temperature of Deep Shallow
water rise in kettle Q.
(ii) The smaller the mass Q2 (a) (i) A wave in which the (b) Refraction of waves
of water, the higher the particles of the medium λ d 3 –1
temperature rise. move in the direction Q2 (a) f = 16 Hz; λ s = ; v d = 6 cm s
2
(iii) The heat supplied must be perpendicular to the λ d λ d
constant. direction in which the wave v s = λ s
(c) The initial temperature of the propagates.
orange juice is higher than the (ii) Water waves Therefore, v s = λ s v d
temperature of the ice cubes. (b) (i) A wave in which the λ d
Heat from the orange juice flows particles of the medium = 2 × 6
to the ice cubes to melt it. The move in the direction 3
heat is continuously absorbed parallel to the direction in = 4 cm s –1
by the cold melting water from which the wave propagates. 4
the ice. The temperature of the (ii) Sound waves (b) λ s = λ s f = 16 = 0.25 cm
orange juice decreased and
the temperature of the cold Q3 (a) Period of oscillation, T = 0.5 s
1
water from the ice increased. (b) Frequency, f = = 1 Q3 (a), (b), (c)
Therefore, orange juice is T 0.5 Direction of
cooled by adding ice cubes. = 2.0 Hz Shallow propagation
(d) • Suggestion: The cup should (c) Wavelength, λ = 5 cm area
be made of good heat (d) Using v = f λ ,
insulator such as polystyrene v = 2.0 x 5 = 10 cm s –1 Normal
material. Deep
Explanation: Good heat Checkpoint 5.2 area
insulation prevents heat from Q1 (a) Q
hot drink being escape by (b) Q has the same natural
conduction. frequency as the vibrating tuning
• Suggestion: The cup cover fork. Hence, Q will receive the Q4
should also be made of good biggest amount of energy from Hotter air
heat insulator such as plastic. the vibrating tuning fork. Speed of sound higher
Explanation: Good insulator (c) Resonance
can prevent heat loss to the
surrounding. Q2 The hand moves with the same Refraction of sound waves occur
• Suggestion: The cup material natural frequency as that of the Source Listener
should also have a high loaded spring. Resonance occurs of s
melting point. and the spring will receive maximum sound
Explanation: So that the cup energy. Colder air
does not easily change its Speed of sound lower
state or melt when filled with Checkpoint 5.3 The diagram shows the temperature
liquid of high temperature. Q1 Let the distance of the wall from the of air at night. The layer of air
• Suggestion: The inside and student be d m above the surface of the Earth is
outside of the cup are coated The distance travelled by sound to colder compared the layer further
with shiny metal. and fro the wall = 2d m away from the surface of the Earth.

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ANS FOC PHYSICF F4 1P.indd 258 29/01/2020 2:04 PM