Define work done by a force. If a force of 10 N moves an object 3 m in the same direction, how much work is done?

• A. 10 J
• B. 3 J
• C. 0 J
• D. 30 J

Answer: (D)

Work is the energy transfer that happens when a force moves an object through a distance in the direction of that force. The amount of work equals the force applied times the distance moved in that direction (W = F × d). Here the force is 10 N and the object moves 3 m in the same direction, so the work done is 10 × 3 = 30 joules. The units Newtons times meters are defined as joules. If the force didn’t align with the motion, or acted opposite to it, the work would be different (zero if the force is perpendicular, negative if it points opposite to the movement, and in general W = F d cos(theta)). In this scenario, the force and displacement align, giving positive 30 J of work.