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GCSE Forces 6.5.1.26.5.4.2.2
~8 min Difficulty: 6/10 8 marks
Prior knowledge massacceleration
Problem structure
3 force marks, 2 weight marks, 3 vector-reasoning marks.

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A 1200 kg car accelerates from rest at 2.5 m/s2. Take g = 9.8 N/kg. (a) Calculate the resultant force on the car. [3] (b) Calculate the weight of the car. [2] (c) Explain why the car can accelerate even though its weight is much larger than the resultant force. [3]
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(a) F = ma = 1200 x 2.5 = 3000 N. (b) W = mg = 1200 x 9.8 = 11 760 N. (c) Weight acts vertically downward and is balanced by the normal contact force; the 3000 N resultant is horizontal and causes the horizontal acceleration.

Marking guidance

Award equation, substitution and values. Explanation requires direction of weight, balancing normal force and horizontal resultant force.