Question

The coefficient of static friction between a concrete block and a surface is 0.8. The block weighs 20 lbf. If a horizontal force of 15 lbf is applied to the block, would the block move? And if not, what is the magnitude of friction force? What should be the magnitude of the horizontal force to set the block in motion?

Answer 1

The block will not move with an applied force of 15 lbf, and the magnitude of the friction force is 15 lbf. A force greater than 16 lbf is required to set the block in motion.

Step-by-step explanation:

First, let's determine if the block will move when a horizontal force of 15 lbf is applied. The maximum static friction force can be calculated by multiplying the coefficient of static friction (0.8) with the normal force (20 lbf). So, the maximum static friction force is 0.8 * 20 = 16 lbf. Since the applied force (15 lbf) is less than the maximum static friction force, the block will not move. Therefore, the magnitude of the friction force is equal to the applied force, which is 15 lbf.

To find the magnitude of the horizontal force required to set the block in motion, we need to compare it with the maximum static friction force. The maximum static friction force is still 16 lbf. So, for the block to start moving, the magnitude of the horizontal force should be greater than the maximum static friction force (16 lbf). Thus, a force greater than 16 lbf is needed to set the block in motion.