1. Work done by a constant force is given by the product of the force and the distance moved in the direction of the force.
  2. The unit of Nm(Newton metre) or J(Joule).
  3. Work is a scalar quantity.


When the direction of force and motion are same, θ = 0o, therefore cosθ = 1
Work done,

W = F × s


A force of 50 N acts on the block at the angle shown in the diagram. The block moves a horizontal distance of 3.0 m. Calculate the work being done by the force.

Work done,
W = F × s × cos θ
W = 50 × 3.0 × cos30o = 129.9J


The diagram above shows a 10N force is pulling a metal. The friction between the block and the floor is 5N. If the distance travelled by the metal block is 2m, find

  1. the work done by the pulling force
  2. the work done by the frictional force

(a) The force is in the same direction as the motion. Work done by the pulling force,
W = F × s
W = (10)(2) = 20J

(b) The force is not in the same direction of motion, work done by the frictional force
W = F × s × cos180o
W = (5)(2)(-1) = -10J

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