JPJC 2026 Forces and Moments Assignment Solutions

2026/JPJC/PHYSICS/9478 1 JURONG PIONEER JUNIOR COLLEGE 9478 H2 PHYSICS FORCES AND MOMENTS ASSIGNMENT SOLUTIONS Total marks: 15 Qn. Solution Mark Allocation 1(a)(i) f: frictional force N: reaction force W: weight [1] correct vector [1] correct label (Any error minus 1 mark) (a)(ii) 5 5 2 2 2 2 5 2 4 (39000)(9.81) 3.83 10 N cos15 39000 3.70 10 N (3900 ) (3.7 10 ) 9.90 10 N W mg NN Wg N N f W fg == = == = += = −  =  [1] [1] [1] 2(b) y , (10)(1.6) (55)(2.8) (5.6) 0 30.4 Taking moments about end A Consider ver kN F tical equilibrium 0 10 55 0 34.6 kN , B B AB A N N NN N + − = = = + − − = =  [1] [1] [1] [1]

2026/JPJC/PHYSICS/9478 2 2(a) W: weight of beam N: normal contact force by bricks on beam R: reaction force by pivot on beam [1] for drawing all three forces [1] for labelling all forces correctly 2(b) As the bricks are moved towards P, the clockwise moment due to the bricks about the pivot O will increase. If the metal beam remains in equilibrium, the anticlockwise moment due to T will also increase so that sum of ACM = sum of CM. The tension T in the cable will increase. [1] [1] 2(c) Applying Principles of Moments about pivot O, ( sin32 )(8.0) 150(9.81)(8.0 5.3) 210(9.81)(4 .0)T  = − + 2900 NT  [1] [1] N R W