AIR RESISTANCE AND TERMINAL VELOCITY
3 marks · EasyExplain why a falling coin eventually stops accelerating and continues to fall at a constant speed. Include what happens to the forces acting on it.
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.
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Must show: Air resistance increases with speed, Eventually air resistance = weight, No resultant force: coin falls at constant speed (terminal velocity)
Also accept: The forces become balanced and the coin moves at terminal velocity
Common mistakes: Not explaining balancing of forces explicitly; Saying the coin stops moving
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States that air resistance increases as the coin speeds up
B2 · 1 mark · States that eventually air resistance balances the weight
B3 · 1 mark · Explains that with no resultant force, acceleration stops and the coin falls at constant speed
Worked solution
As the coin falls, its speed increases and air resistance grows.
Eventually, the air resistance force equals the weight of the coin.
At this point, the forces are balanced, so the coin no longer accelerates and falls at a constant speed—this is terminal velocity.