Question detail
If a 3 kg object is lifted to a height of 8 m, what is the gravitational potential energy gained?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Energy changes in a system, and the ways energy is stored before and after such changes
Question
- A. 120 J
- B. 240 J
- C. 300 J
- D. 2400 J
Answer
240 J
Explanation
The correct option is "240 J". 240 J is right because it directly matches Changes in energy: Calculate gravitational potential energy gained by an object raised above ground level.. The other options are less suitable because they change the required Physics relationship, confuse the relevant energy store or use a distractor that does not answer the question.
Common mistake
Confusing gravitational field strength with acceleration due to gravity
Students often use g = 9.8 m s⁻² as the gravitational field strength in the formula Ep = m g h, but g is the acceleration due to gravity, not the field strength. They then treat g as a unitless constant and ignore that the field strength can vary with location or be given explicitly in the problem.
Remind students that the gravitational field strength (g) is the force per unit mass and has units of N kg⁻¹ (or m s⁻²). In the formula Ep = m g h, g is the field strength, so it must be supplied or calculated from the local value of g. If the problem states the field strength directly, use that value; if it only gives the acceleration due to gravity, treat it as the field strength for the calculation. Always keep the units consistent: m (kg) × g (N kg⁻¹) × h (m) = J.
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