Page 64 - Q & A STPM 2022 Physics

Physics STPM Answers
13. D: XY:Q = ∆U + W, Q = 0
∆U = –W = –15 J
At Y, U = (50 – 15) J = 35 J

Temperature at X and Z is equal. U = U = 50 J
x z
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YZ: Q = ∆U + W, W = 0
= U – U + 0
Z Y
= (50 – 35) J = +15 J
14. D: Stefan’s law: P = eσAT 4 Semester
k (q – 40)/2l
15. B: = gives
2k (100 – q)/l 1
Temperature at junction, q = 70°C

Section B
16. (a) (2.5 + 1.5)v = (2.5)(0.50) – (1.5)(0.30)
v = 0.20 m s
–1
(b) (2.5)v + (1.5)v = (2.5)(0.50) – (1.5)(0.30)
2
1
1
1
1
1 (2.5)v + (1.5)v = (2.5)(0.50) + (1.5)(0.30) 2
2
2
2
2 1 2 2 2 2

Alternative method:
(2.5)v + (1.5)v = (2.5)(0.50) – (1.5)(0.30)
1 2
Newton’s law of restitution:
v – v = –[0.50 – (–0.30)]
2
1
Solving, = –0.10 m s , v = 0.70 m s –1
v
–1
1 2
E A E A
17. (a) F = ( Cu l )e = ( Fe )e Fe
Cu
2l
e
e Cu = 1.0
Fe
(b) F = k e = k e
Cu
Cu
Fe Fe
k
Cu = 1.0
k Fe
e F
(c) (Strain) = Cu =
Cu
l E A
F
e Cu
(Strain) = Fe =
Fe 2l E A
Fe
(Strain) / (Strain) = 2
Cu Fe
1
(d) Strain energy = Fe
2
(Strain energy) = (Strain energy)
Cu Fe

537
ANS STPM Q&A Physics.indd 537 16/02/2022 4:35 PM