AIR RESISTANCE AND TERMINAL VELOCITY
4 marks · NormalA supply crate of mass 75 kg is dropped by parachute onto a remote island. The gravitational field strength is 9.8 N/kg.
Calculate the weight of the crate.
The parachute opens and the crate reaches a terminal velocity of 5 m/s. State what this tells you about the forces acting on the crate as it descends at this speed.
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) 735 N · must show W = m × g
(b) At terminal velocity, the upward force from air resistance (plus parachute) equals the weight downward. The forces are balanced. · must show Upward force equals weight, Forces are balanced
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Substitutes values correctly into W = m × g.
A1 (a) · 1 mark · Correct answer (735 N) with correct unit.
B1 (b) · 1 mark · Identifies that at terminal velocity, air resistance plus parachute equals weight.
B2 (b) · 1 mark · States that the forces are balanced.
Worked solution
At terminal velocity, the force due to air resistance (with the parachute) upwards is equal to the weight of the crate downwards. There is no net force so the crate descends at constant speed.