A block is pulled along a horizontal surface with a constant horizontal force of magnitude . The surface exerts a frictional force of constant magnitude on the block. The graph of speed as a function of time for the block is shown above.
If, instead, the block slides without friction but is pulled with the same horizontal force of magnitude , which of the following would be a possible new graph of speed as a function of time ? (The dashed line represents the old graph.)
Select an Answer
The correct answer is (A). Without friction, there is still a constant force on the block. This means a constant acceleration, so the speed curve will still be a straight line. Removing friction will not cause the block to be in motion before it is pulled, so the initial speed remains zero. Finally, since friction would act against the pulling force, the net force on the block is greater without friction, so the acceleration and thus the slope of the speed graph would be greater