Energy, Work and Power: Question 5

Syllabus 1.7.4

Multiple choice Core 1 mark

A weightlifter raises a barbell, transferring $750\text{ J}$ of energy to the gravitational potential energy store of the barbell in $2.5\text{ s}$ . What is the useful power developed by the weightlifter during the lift?

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Step 1: Recall the equation for power

Power is the energy transferred per unit time:

$P = \frac{E}{t}$

Step 2: Substitute the values

$P = \frac{750\text{ J}}{2.5\text{ s}}$

Step 3: Work out the answer

$P = 300\text{ W}$

Why the other options are wrong

Option	How it arises	Error
$1875\text{ W}$	$750 \times 2.5$	Multiplied instead of dividing
$0.0033\text{ W}$	$2.5 \div 750$	Formula inverted (time ÷ energy)
$747.5\text{ W}$	$750 - 2.5$	Subtracted instead of dividing

Final answers

Power $= \boxed{300\text{ W}}$ , option D