Power

3 marks · Normal

A lift with passengers has a combined weight of 3500 N. The lift rises vertically at a constant speed of 2.5 m/s.

(a)

State the upward force needed to keep the lift moving at constant speed.

[1 mark]

(b)

Calculate the power output of the lift motor.

[2 marks]

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) 3500 N

(b) 8750 W

Common mistakes: Not using correct force for constant speed

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · States upward force equals lift weight (3500 N)

M1 (b) · 1 mark · Substitutes values into P = Fv (follow-through)

A1 (b) · 1 mark · Correct power output value (8750 W, or correct follow-through) (follow-through)

Worked solution

a) Upward force must equal the weight to maintain constant speed: 3500 N.

b) Power output = force × velocity: