O-LevelPhysicsForces5054/21 · Oct/Nov 2016 · Q26 Marks
Fig. 2.1 shows a bed that folds away against a wall during the day. [Figure 2.1] When it is horizontal, the bed is supported on one side by a hinge and on the other side by two legs. The weight W of the bed acts through its centre of mass, which is at a horizontal distance of 0.35 m from the hinge.
- (a)The mass of the bed is 26 kg. The gravitational field strength g is 10N/kg. Calculate the weight W of the bed.[1]
- (b)(i)State the principle of moments.[2]
- (b)(ii)Determine the size of the total upward force exerted on the bed by the two legs when the bed is horizontal.[3]
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Mark scheme
Marking points from the official mark scheme (Oct/Nov 2016). The mark or mark type is shown in brackets.
- [B1] 260 N
- [B1] for a body in equilibrium
- [B1] (total) clockwise moment = (total) anticlockwise moment
- [C1] F₁d₁ = F2d2 or 260 × 0.35 or 91 or F × 0.65
- [C1] 260 x 0.35 = F × 0.65 or 260 × 0.35/0.65 or 91 = F × 0.65 or 91/0.65
- [A1] 140 N
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