FORCE, MASS AND ACCELERATION
4 marks · HardA football goalkeeper of mass 80 kg dives to stop a ball and comes to a stop in 0.15 s after making contact with the ground. Just before contact, the goalkeeper's horizontal speed is 5.2 m/s.
Calculate the horizontal acceleration of the goalkeeper as he comes to rest.
Calculate the magnitude of the unbalanced force acting on the goalkeeper during this time.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) -34.67 m/s^2
(b) -2773 N
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Substitutes correct values into the acceleration formula:
A1 (a) · 1 mark · Correct final answer for acceleration, to 2 significant figures; signs (direction) may be ignored
M2 (b) · 1 mark · Uses with the mass and acceleration from part a (follow-through)
A2 (b) · 1 mark · Correct value for the force (to 2/3 significant figures, units N) (follow-through)
Worked solution
a) Initial velocity m/s, final velocity (comes to rest), time s.
Acceleration = m/s² (2 s.f.)
b) Using , mass kg, m/s²
The magnitude of the unbalanced force is 2770 N (2 s.f.).