A 150 N block is at rest on a table, a cable is connected from this block to another hanging off of the table. This block is 75 N. What is the magnitude of the minimum force of static friction on the 150 N block required to hold both blocks at rest?

Question

A 150 N block is at rest on a table, a cable is connected from this block to another hanging off of the table.  This block is 75 N.  What is the magnitude of the minimum force of static friction on the 150 N block required to hold both blocks at rest?

What would the coefficient of static friction between the 150 N block and the table have to be to ensure that both blocks would be held at rest?

I know the answers are 75 N  and .5, but i need an explanation on how to get these answers!

bbwake · Accepted Answer

1. To balance the gravity of the 75N block, the pull force from the cable applied on it should be 75N.
2. Then the cable pulls the 150N block with a force of 75N.
3. To balance the pull force from the cable, the static friction should be 75N.
4. And the coefficient of static friction is 75/150=0.5