O-LevelPhysicsEnergy & Work5054/21 · Oct/Nov 2022 · Q27 Marks

A child's toy consists of a flexible track and a model car. Fig. 2.1 shows a diagram of the toy. The child first holds the car stationary at point A which is 0.45m above the horizontal sections of track BC and FG. The mass of the car is 0.12kg. The child then releases the car which travels towards point B. Both air resistance and friction between the car and the track are negligible. The gravitational field strength g is 10N/kg.

(a)Calculate the change in gravitational potential energy (g.p.e.) of the car as it travels from A to B.[2]
(b)Calculate the speed of the car when it reaches B.[3]
(c)(i)Explain, in terms of energy, why the car does not go past D, which is also 0.45m above the horizontal track.[1]
(c)(ii)Immediately after being released at A, the car travels to B, to C and then to D. Describe the motion of the car after it reaches D.[1]

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Mark scheme

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

[1] (change in g.p.e.=) mgh or 0.12 × 10 × 0.45
[1] 0.54 J
[1] k.e. = ½mv² or 0.54 = ½ × 0.12 x v²
[1] (v =) √2gh or √2 10 0.45 or v² = 2 × 0.54 / 0.12 or v ² = 9
[1] 3.0 m/s
[1] not enough (kinetic) energy (at C) to travel beyond D / to top of circle or more g.p.e. needed originally to travel beyond D/ to top of circle or g.p.e. gained cannot be greater than original g.p.e. (transferred to k.e)
[1] it travels back down to C and returns to A

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