This document contains the answers to multiple choice and free response physics problems about forces and moments: 1. It provides the answers to 3 multiple choice questions. 2. Questions 4-7 contain worked solutions to problems involving forces, vectors, and moments. Diagrams are included. 3. Questions 8-9 involve calculating tensions, reaction forces, and distances using moments, lever arms, and equilibrium conditions. Worked calculations with multiple steps are shown.

1. 4 Marking scheme: Worksheet (AS)
1 D [1]
2 D [1]
3 C [1]
4 a R2 = 7.02 + 5.02 [1]
R = 49 25 = 8.6 N [1]
b Force vertically = 40 10 = 30 N and force horizontally 80 20 60 N [1]
R2 = 302 + 602 [1]
R 900 3600 67 N [1]
5 a Fx = F cos = 10 cos 45°
Fx 7.07 N 7.1 N [1]
Fy = F sin = 10 sin 45°
Fy 7.07 N 7.1 N [1]
b Fx = F cos = 85 cos 20°
Fx 79.9 N 80 N [1]
Fy = F sin = 85 sin 20°
Fy 29.1 N 29 N [1]
6 a The net force is zero because the seat is in equilibrium. [1]
b i
Correct diagram [1]
Weight = mg = 35 9.81 343 N [1]
T2 = 1802 + 3432 [1]
T 1802 3432 390 N [1]
180
ii tan = [1]
343
tan 1 (0.525) 28 [1]
7 a Fx = F cos = 300 cos 30º [1]
Fx 260 N [1]
b The net force is zero, because the roller is moving at constant velocity. [1]
Resistive force 260 N to the left. [1]
c Fy = F sin = 300 sin 30° = 150 N [1]
AS and A Level Physics Original material © Cambridge University Press 2010 1

2. 4 Marking scheme: Worksheet (AS)
The net vertical force is zero.
150 + contact force = mg [1]
contact force = (50 9.81) 150 340 N [1]
8 a The line of action of the weight of the ladder is at a perpendicular distance of 0.75 m away
from the foot of the ladder.
Taking moments about the base of the ladder
sum of clockwise moments = sum of anticlockwise moments [1]
(32 9.81) 0.75 = R 4.0 [1]
32 9.81 0.75
R 59 N [1]
4.0
b The force at the base of the ladder creates zero moment about this point. [1]
9 a All forces clearly shown on
the diagram. [2]
b Taking moments about the brick
sum of clockwise moments = sum of anticlockwise moments
(62 9.81)x + (15 9.81) 0.78 = (30 9.81) 1.56 [2]
(1.56 30) (0.78 15)
x 0.57 m [1]
62
x 0.57 m
Distance of centre of gravity from the toes = 1.56 0.57 = 0.99 m [1]
AS and A Level Physics Original material © Cambridge University Press 2010 2