O-LevelPhysicsForces5054/22 · Oct/Nov 2023 · Q29 Marks

A spacecraft of mass 300kg is moving in a straight line in space, at a speed of 8000m/s.

(a)Calculate the momentum of the spacecraft. momentum = .......................... kgm/s[2]
(b)(i)The fuel on the spacecraft explodes and the spacecraft splits into two parts. The direction in which the parts move does not change. After the explosion, the speed of the front part increases to 9000m/s. It has a mass of 150 kg. Calculate the speed of the rear part after the explosion. speed = .......................... m/s[3]
(b)(ii)The total kinetic energy of the two parts after the explosion is greater than the original kinetic energy of the spacecraft. State the energy transfer that occurs in the explosion.[1]
(b)(iii)The explosion lasts for 0.20s. Calculate the average force on the front part during this time. force = .......................... N[3]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

[1] (p =) mv or 300 × 8000
[1] 2.4 x 10⁶ (kg m/s)
[1] momentum conserved or mv = m₁V₁ + m₂V₂
[1] (v₂ =) (2.4 × 10⁶ – (150 × 9000)) ÷ 150 or (v₂ =) (1 050 000) / 150
[1] 7000 (m/s)
[1] from energy stored as chemical (potential) energy
[1] Ap or J or I = 150 × (9000 – 8000) or 150 000 or (a =) (9000 – 8000) ÷ 0.20 or (a =) 5000
[1] (F =) Ap/(A)t or (F =) I/ (△)t or (F =) ma or 150 × (9000 – 8000) / 0.20 or 150 × 1000/0.20
[1] 7.5 × 10⁵ (N)

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