In the Diagram Below, a Force Acting on a Block

Multiple Choice

In the diagram below, a force acting on a block is shown by the arrow labeled F. The mass of the block is known, as is the size of the force, but the observed acceleration is larger than F/m and so another force must act on the block. In which direction (A, B, C, or D) is this force?

A) A
B) B
C) C
D) D