Page 65 - Q & A STPM 2022 Physics

Physics STPM Answers
Section C
18. (a) Centripetal force: force towards the centre of the circle that enables the particle
to move in a circle.
Reason for the acceleration:
• direction of velocity is constantly changing
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• acceleration = rates of change of velocity
(b) (i)
Friction, F  Reaction, R

Semester
1 Weight, mg
(ii) F = μR
R sin 30° + (μR) cos 30° = mg
(0.050)(9.81)
R = N = 0.481 N
sin 30° + (0.60)cos 30°
(iii) Friction = μR = 0.289 N
(iv) R cos 30° – F sin 30° = (0.050)r[2(2.5)π] 2
(0.481)cos 30° – (0.289)sin 30°
Radius, r = m
(0.050)(5.0π) 2
= 2.20 cm
(v) Centripetal force, R cos 30° – F sin 30° = constant
= mrw 2
When r decreases, w increases.
19. (a) (i) n : number of gas molecules per unit volume
m : mass of gas molecule
<c >: mean square speed of gas molecules
2
1 1 1 M
(ii) p = nm<c > = ρ<c > = <c >
2
2
2
3 3 3 V m
1
pV = (mN )<c >= RT
2
m 3 A
3
3 R
1
Mean translational K.E. = m<c > = ( )T = kT
2
2 N
2
2
A
(b) (i) p (iii) I: W= p (2V – V ) = p V
o 0 0 o 0
I 2V
II: W = nRT ln ( 0 ),
0
II V 0
p V = nRT 0
o
0
III
0 V W = p V ln2
o
0
V 0 2V 0
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ANS STPM Q&A Physics.indd 538 16/02/2022 4:35 PM