The diagram shows equipotential lines for a uniform gravitational field - AQA - A-Level Physics - Question 13 - 2021 - Paper 2

To calculate the work done against gravity when moving the object from point P to Q, we first need to find the change in gravitational potential.

From the diagram:

• The potential at Q is given as (V + 3) J kg⁻¹.
• The potential at P is (V) J kg⁻¹.

The change in gravitational potential, ΔV, is:

$$ΔV = (V + 3) - V = 3 ext{ J kg}^{-1}$$

Next, we apply the formula for work done against gravity:

$$W = m imes ΔV$$

where:

• m is the mass of the object (4 kg)
• ΔV is the change in gravitational potential (3 J kg⁻¹)

Substituting the values, we get:

$$W = 4 ext{ kg} imes 3 ext{ J kg}^{-1} = 12 ext{ J}$$

Therefore, the work done against gravity to move the object from P to Q is 12 J.