A boy lifts a 20 kg mass vertically at a constant speed of 5 m/s. If the acceleration due to gravity is 10 m/s², calculate the power developed by the boy.

• Mass of the object, $m = 20 \text{ kg}$
• Velocity, $v = 5 \text{ m/s}$
• Acceleration due to gravity, $g = 10 \text{ m/s}^2$

In a single string pulley system, to lift a mass at a constant velocity, the force applied must be equal to the weight of the mass.

Power ($P$) is the product of force ($F$) and velocity ($v$).

The power developed by the boy is $1000 \text{ W}$.

The correct option is D) 1000W.