A constant force of 10 N acts on a 5 m displacement in the opposite direction to the motion. What is the work done by the force?

A constant force of 10 N acts on a 5 m displacement in the opposite direction to the motion. What is the work done by the force?

• A. -50 J
• B. -10 J
• C. 50 J
• D. 0 J

Answer: (A)

Work is the energy transferred by a force acting through a displacement, and it depends on how much of the force acts in the same direction as the displacement. When the force is opposite to the motion, the component along the displacement is negative. So the work is W = F d cos(theta) with theta = 180°, giving W = 10 N × 5 m × cos(180°) = 50 × (-1) = -50 J. The negative sign means this force removes energy from the moving object, reducing its kinetic energy by 50 joules. If the force were in the same direction as the motion, it would do positive work and increase the kinetic energy.

Work is the energy transferred by a force acting through a displacement, and it depends on how much of the force acts in the same direction as the displacement. When the force is opposite to the motion, the component along the displacement is negative. So the work is W = F d cos(theta) with theta = 180°, giving W = 10 N × 5 m × cos(180°) = 50 × (-1) = -50 J. The negative sign means this force removes energy from the moving object, reducing its kinetic energy by 50 joules. If the force were in the same direction as the motion, it would do positive work and increase the kinetic energy.