O-LevelPhysicsForces5054/22 · Oct/Nov 2021 · Q27 Marks

Force is a vector quantity.

(a)State what is meant by a vector.[1]
(b)(i)The swimmer pushes against the end wall of the pool with his legs. Explain, in terms of Newton's third law, why the swimmer accelerates away from the end wall.[3]
(b)(ii)While swimming, there is a constant forward force on the swimmer. His speed increases until eventually he reaches a constant speed. Explain why he reaches a constant speed.[3]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

[B1] (a vector quantity has) magnitude and direction
[B1] the wall exerts a force on swimmer
[B1] opposite in direction (to force of swimmer on wall) or to the right
[B1] equal in size (to force of swimmer on wall) or (resultant) force causes acceleration or force on object Y due to X is equal and opposite to force on object X due to Y
[B1] (water) resistance / resistive force / friction (on swimmer)
[B1] (water) resistance / backward force / resistive force / friction / opposing force increases (with speed / time)
[B1] (at constant speed) forward force is equal to resistive / backward force OR no resultant force or forces balance

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