Page 64 - Focus TG4 KSSM (Physics) Terbitan Penerbitan Pelangi Sdn Bhd

Physics Form 4 Answers

• The time interval for the (iii) The cartwheel must be large Mass, m = 200 g = 0.2 kg
signal or echo to arrive is in diameter. So that cart Using, Q = mcDq
recorded. can be easily move and Therefore, specific heat
• From ultrasonic velocity, the pushing force can be capacity of, X,
2d reduced.
v = , depth is calculated Q 6 000
t vt (iv) The cartwheel should made c = =
using the formula d = . of hard rubber. So that the mDq 0.2 × 40
2
–1
(d) (i) The speakers should be cart can be easily move and = 750 J kg °C
not easily damaged when
arranged in such a way that carrying heavy goods. (ii) Time taken, t
no sound wave interference The L trolley is the perfect = 8 – 4 = 4
occurs so that the same choice because it has the right = 4 × 60
loudness can be heard in all height of handle, light and strong = 240 s
directions. base, large wheel diameter and
(ii) The speaker must be made of hard rubber Heat supply, Q
powerful enough to (d) (i) Change in velocity = 25 × 240
transmit sound waves in = –22 + –25 = 6 000 J
all directions so that sound = –47 m s –1 Mass, m = 200 g = 0.2 kg
can be heard clearly and (ii) Average acceleration Using, Q = mL
in all directions with equal Change in velocity Therefore, specific latent
loudness. a = Time taken heat of fusion of X,
(iii) A good amplifier along with 47 Q 6 000 J
a good microphone is used = 0.0013 L = m = 0.2 kg
so that a person›s voice = 3.6 × 10 4 = 30 000 J kg –1
can be clearly detected and (iii) Average force,
amplified. F = m × a (c) • The cover should be made
(iv) The walls of the concert hall = 0.16 × 3.6 × 10 4 of hollow plastic. Air trapped
should be fitted with small = 5 760 N in hollow plastic is a good
hollow soft boards so that thermal insulator and can
sound waves can be fully 12. (a) (i) The specific latent heat of prevent heat lost to the
absorbed without reflection. vaporisation of water is the surrounding.
The floor should be amount of heat required to • Space P should be a vacuum.
carpeted to avoid sound convert 1 kg of water into The vacuum can prevent heat
wave reflection. steam without temperature lost through conduction and
change. convection.
Section C (ii) Water has a large specific • Two-layer wall must be made
latent heat of vaporisation. of glass. Glass is a good
11. (a) Impulse is change in momentum When steam condenses it
(b) When the player hits a tennis releases a large amount insulator of heat and has a
ball, he or she can increase the of heat. Foods like fish in greater specific heat capacity.
contact time with the racket. a plate can absorb a lot of This feature can reduce heat
This will add impulse to the ball heat from hot steam. The transferred to the surrounding.
and increase the momentum food becomes cooked when • The wall should be coated
change on the ball. Therefore, the food reaches thermal with shinny paint. The shiny
the speed of the tennis ball equilibrium with the steam surface is a good heat
increases. after some time. reflector and can reduce heat
(c) (i) The height of the handle (b) (i) Time taken, t = 4 min loss.
should be approximately the = 4 × 60 s • The thermos flask S is the
height of the shoulder of the = 240 s best choice because it uses
pusher. So that the cart is hollow plastic as cover, the
easy to push. Lower handle Change in temperature, DT space P is vacuum, the two-
needs more force to push. = 60° – 20° layer wall made of glass and
(ii) The base of the cart should = 40°C coated with shiny paint.
be light and strong. So that Heat supplied, Q
the cart is easily push and = P × t
the hard material is not = 25 × 240
easily damaged and can = 6 000 J
last longer.

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ANS FOC PHYSICF F4 1P.indd 265 29/01/2020 2:04 PM