O-LevelPhysicsEnergy & Work5054/21 · Oct/Nov 2015 · Q36 Marks
A lorry of mass 4.4 × 10⁴ kg travels along a straight, horizontal road at 20m/s.
- (a)Calculate the kinetic energy of the lorry. kinetic energy = [3]
- (b)(i)The lorry driver sees an obstruction ahead and applies the brakes. The lorry slows down and stops. The lorry stops a distance of 40m from where the driver first applies the brakes. As it slows down, the kinetic energy of the lorry decreases to zero. The kinetic energy decreases as work is done by the braking force exerted on the lorry. State the formula that relates the work done to the braking force.[1]
- (b)(ii)Calculate the braking force exerted on the lorry. force = [2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2015). The mark or mark type is shown in brackets.
- [1] (k.e. = )½mv²
- [1] ½ x 4.4 x 10⁴ x 20²
- [1] 8.8 × 10⁶ J
- [1] WD = F × x or force × distance (parallel to/in direction of force)
- [1] 8.8 × 10⁶/40 or a = (−)5.0 (m/s²) or t = 4.0 (s) seen
- [1] 2.2 × 10⁵ N
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