A student must determine the work done on an object when an external force is exerted on it after it travels a specific distance. An external force is exerted on an object at position x by a string as the object moves a distance d across a horizontal surface for a time t. The force changes such that it decreases as the object moves. Which procedure could be used to determine the work done on the object by the external force?
a) Calculating the area under the force-distance graph
b) Multiplying the force by the displacement
c) Dividing the force by the distance traveled
d) Integrating the force function over the distance traveled
