Question 5
FrictionA brick at rest on a horizontal table is pulled by a horizontal cord, as shown in Fig. 2. The force of friction on the brick
- A.increases if the pull increases but the brick does not move
- B.is directly horizontal to the right
- C.decreases if an identical brick is placed on the first
- D.is zero if the brick is pulled hard enough to make it slide
- E.change if the brick is turned on its side.
Show the answer and explanation
Answer: A (increases if the pull increases but the brick does not move)
Explanation
Static friction always matches the pull up to its limiting value, so while the brick stays still a bigger pull is met by a bigger friction force.