O-LevelPhysicsForces5054/22 · May/June 2022 · Q18 Marks

Fig. 1.1 shows a waterskier pulled horizontally across the water surface. [Figure 1.1] The mass of the waterskier is 60 kg. The gravitational field strength g is 10 N/kg.

(a)Calculate the weight of the waterskier.[1]
(b)Mass and weight have different units. State two other differences between mass and weight.[2]
(c)(i)A boat pulls the waterskier to the right with a horizontal force of 50 N. The waterskier travels at a constant speed. Explain, in terms of the horizontal forces acting, why the speed is constant.[2]
(c)(ii)The horizontal force acting to the right increases from 50 N to 70 N. The sizes of any other forces are unchanged. Calculate the acceleration of the waterskier.[3]

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Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

[1] 600 N
[2] ANY 2 separate bullet points from: weight is a vector / weight has direction / mass has no direction / mass is a scalar; mass is the amount of matter / substance; weight is a force / weight is mass × gravitational field strength; weight varies with position (of object) / gravitational field (strength) / mass does not vary with position; mass resists change of motion / has inertia
[1] friction (with water) or drag or air/water resistance mentioned
[1] (forces) balance / cancel or no resultant force
[1] (resultant force) 20 (N) or 70 – 50 seen
[1] (a =) F/ m algebraic or numerical in any form
[1] 0.33 m/s²

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