Work and Power
6 marks · NormalA construction worker lifts a toolbox of mass 12 kg vertically upwards at a steady speed through a height of 2.5 m in 5 seconds.
Calculate the work done by the worker in lifting the toolbox.
State the relationship between work done and energy transferred in this process.
Calculate the power output of the worker while lifting the box.
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) 300 J
(b) Work done is equal to the energy transferred.
(c) 60 W
Common mistakes: Using mass instead of weight for force; Dividing by wrong time interval; Confusing units
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correct formula: W = F × d or W = mgh used
A1 (a) · 1 mark · Correct numerical work done (accept rounding of 300 J) (follow-through)
B1 (b) · 1 mark · States work done is equal to energy transferred
M2 (c) · 1 mark · Uses P = W/t with correct values (allow ft from (a)) (follow-through)
A2 (c) · 2 marks · Correct power output in W, accept 60 W with rounding; must include units (follow-through)
Worked solution
a) First, calculate the force (weight):
Work done:
b) The work done on the toolbox is equal to the energy transferred to it.
c) Power output is calculated by dividing work by time: