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Physics Form 4 Answers

(c) the air resistance is balanced by (d) Size of image formed does not • the increase in air
the weight of the skydiver. change, but the brightness of temperature in Diagram
3. (a) • The force holding the satellites the image formed is less. 9.1 is smaller.
and the Moon in their orbit is 7. (a) Heat is a formed of energy. (ii) The temperature increases
the gravitional force. (b) (i) The thermometer reading in as the heat supplied
T 2 increases. As the air
• The ratio R 3 for all satellites is Diagram 7.1 is higher. temperature increases, the
a constant. (ii) The volume of water in air pressure in the flask
Diagram 7.2 is larger.
R 3 (386 000) 3 (iii) The time taken to heat the increases.
(b) 2 = (c) According to kinetic theory, the
T (27 × 24) 2 water is the same, which is kinetic energy of gas molecules
=1.37 × 10 km jam –2 5 minutes. increases as heat is absorbed.
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(c) (i) The smaller the volume of
(R E ) 3 The air molecules in the flask
(c) 2 = 1.37× 10 11 water, the larger the reading move faster and collide more
24 of the thermometer.
R E = 1.37 × 10 × 24 2 (ii) The smaller the mass of frequently with the flask wall and
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thus increases the air pressure
R E = 42 892 km water, the higher the rise in in the flask.
4. (a) Water vapour temperature. (d) (i) The sheath mass should be
(b) The heat energy supplied (d) (i) Amount of heat supplied, small and light so that the
is used to release the water Q = 16 × (1 × 60 × 60) aneroid barometer is easy
molecules into the air. The = 57 600 J to carry.
kinetic energy of the molecules (ii) Q = mcDq (ii) The chamber should be
does not change. 57 600 = 0.8 × 4 200 × Dq made of light metal box
(c) Heat used to change 20 g of DT = 57 600 enclosed with corrugated
water to steam, 0.8 × 4 200 edges so that it is flexible
Q = 52 000 – 6 000 = 17.1°C and can move up or down.
= 46 000 J The air in the chamber
Mass of water change to steam, 8. (a) (i) Velocity is the rate of is released into a partial
m = 20 g = 20 × 10 kg change of displacement vacuum, so that the space
–3
Specific latent heat of or distance move in one can respond to changes
vaporisation, second in a specific in the outside air pressure
direction.
more effectively.
L = Q (ii) Velocity change because its (iii) Spring must be strong
m
= 46 000 –3 direction change. and easily extend in order
20 × 10 (iii) Force of gravity towards to respond well to the
–1
= 2.3 × 10 J kg the centre of Earth. This movement of the chamber.
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force produces centripetal
(d) When water evaporates, force perpendicularly to the (iv) The lever should be light
the water molecules acquire direction of motion. and easy to move in order
energy and change into vapour (b) (i) Resultant force to simplify the movement of
and leaves the less energy = Upthrust – rocket weight the chamber and pointers.
molecules behind. This reduces Upthrust 10. (a) A sound wave is a kind of
the average kinetic energy of = 50 000 N + 40 000 × 10 N longitudinal wave, produced
the molecules and thus the = 450 000 N from vibrating object in which
water is cooled down. (ii) Resultant force, F = ma the particles in the medium
5. (a) transverse wave 50 000 = 40 000 × a move forward and backward
(b) • same frequency 50 000 in the direction of the wave
• λ d > λ c Acceleration, a = 40 000 propagation.
(c) • λ d = 1.5 cm = 1.25 m s –2 (b) (i) The distance x in Diagram
• λ c = 1.0 cm (c) (i) 10.1 is smaller than the
(d) v = fλ = 5.0 × 1.0 = 5.0 cm s –1 Velocity distance x in Diagram 10.2.
(e) The distance a in Diagram
10.1 is smaller than the
distance a in Diagram 10.2.
The larger the value of a,
Deep Shallow the smaller value of x.
region region (ii) The distance D, between
0 2 4 6 8 10 12 the speaker and the
Time after launching / min interference pattern, must
6. (a) Refraction of light be constant. The physical
(b) (i) Thickness of lens P < (ii) Area under the graph phenomenon is interference
thickness of lens Q Section B of sound wave.
(ii) f 1 > f 2 9. (a) To measure gas presure (c) (i) Sound waves with
(iii) h 1 > h 2 (b) (i) • the reading of Bourdon frequencies exceeding
(c) (i) The thicker the lens, the gauge in Diagram 9.1 is 20 kHz are called ultrasonic
shorter the focal length. smaller. waves.
(ii) The longer the focal length, • the heat supplied to (ii) • Ultrasonic signals are
the smaller the size of Diagram 9.1 is smaller. transmitted into the sea
image formed. until reaches the sea floor.
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ANS FOC PHYSICF F4 1P.indd 264 29/01/2020 2:04 PM