The following question was on a quiz in physics class:
If the net work done on a particle is zero, which of the following statements must be true?
a) The velocity is zero
b) The velocity is decreased
c) The velocity is unchanged
d) The speed is unchanged
e) There is no displacement for the object
The correct answer was e. In what scenario would the speed change?
There was an explanation beside the question:
Since the work done is zero, it indicates that the applied force is zero. Since Force = Mass X Acceleration, and the mass is not zero, this implies that the acceleration is zero.
When asked about this question, the teacher responded:
If there is no displacement, then only work done is zero. If the speed is unchanged, then there is no acceleration. This will lead to an absence of a force. Hope it explains the situation.