O-LevelPhysicsEnergy & Work5054/21 · Oct/Nov 2019 · Q27 Marks

A small coin of mass m is initially at rest. It is dropped from a height h above ground level. The coin has a speed v as it hits the ground. The gravitational field strength g is equal to 10N/kg.

(a)State an expression for: • the gravitational potential energy of the coin at a height h above ground level gravitational potential energy = • the kinetic energy of the coin when travelling at a speed v. kinetic energy =[1]
(b)The coin is dropped from the top of a building of height 380 m. Determine the speed of the coin as it hits the ground. You may ignore air resistance.[3]
(c)(i)When air resistance is negligible, a heavier coin hits the ground at the same speed as a lighter coin when they are both dropped from the same height. Explain why.[1]
(c)(ii)When air resistance acts, coins of different masses do not hit the ground at the same speed when they are dropped from the same height. Explain why.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

[B1] mgh and 1/2 mv²
[C1] 1/2 mv² =mgh or v² = 2gh or v² =2 x 10 x 380 or v² = 7600
[C1] (v =)√2gh or √2×10×380
[A1] 87 m/s
[B1] both the g.p.e. and the k.e. are proportional to mass or mass cancels out in the equation or they accelerate at the same rate/g
[B1] air resistance (force) is a smaller proportion of weight (for heavier coin)
[B1] acceleration of heavier coin greater / less affected by air resistance

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