O-LevelPhysicsEnergy & Work5054/21 · Oct/Nov 2018 · Q46 Marks

A rock from space is travelling at high speed towards the Earth.

(a)Complete the equation for the kinetic energy of an object travelling with a speed v and state what any other terms in the equation represent. kinetic energy = [1]
(b)(i)The mass of the rock is 0.60 kg. When it hits the Earth, its average temperature increases by 25°C. The specific heat capacity of the rock is 560J/(kg°C). Calculate the increase in the internal energy of the rock. increase in internal energy = [2]
(b)(ii)Use the answer from (b)(i) to determine the minimum possible speed of the rock when it hits the Earth. minimum speed = [2]
(b)(iii)Suggest one reason why the speed determined in (b)(ii) is less than the actual speed of the rock when it hits the Earth.[1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[B1] (kinetic energy =) ½mv² and m is the mass of the object
[C1] (∆Q =) mc∆T or 0.60 × 560 × 25
[A1] 8.4 x 10³ J
[C1] v² = 2∆Q/ m or 8.4 × 10³ = ½ × 0.60 × v² or (v² =) 2.8 × 10⁴ (m²/s²)
[A1] 167 m/s
[B1] some internal / thermal energy lost (to ground / air) or work done to shatter rock
[B1] or rock bounces or energy used to compress ground or rock melts

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