Calculate the gravitational potential energy gained by a 5 kg object raised to a height of 10 m. Use the equation Ep = m x g x h, where g = 9.8 N/kg.

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.