O-LevelPhysicsForces5054/22 · Oct/Nov 2017 · Q15 Marks

Two small tugboats are pulling a large ship in a harbour. [Figure 1.1] represents the view from above and shows the directions of the forces on the ship. Each of the tugboats is exerting a force of 49 kN on the ship.

(a)Determine by a graphical method the resultant of these two forces and state the scale used.[3]
(b)The engines of the ship are not operating and the water in the harbour is stationary. The ship is moving in a straight line in the direction of the total force exerted by the tugboats. It is travelling at a constant speed. Explain, in terms of the forces acting, why the ship is moving in a straight line at constant speed.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

[B1] scale at least: 1.0cm: 10 kN
[B1] correct triangle or correct parallelogram and resultant, i.e. (diagrams showing vector addition)
[B1] 90 kN < resultant < 94 kN
[B1] no resultant force or balanced forces or all forces cancel
[B1] (force of tugboats cancelled) by drag/water resistance/water friction etc.

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