To find the force of friction that does work on the block, we need to calculate the force exerted by the spring on the block.
We can use Hooke's law, which states that the force exerted by a spring is directly proportional to the displacement from its equilibrium position.
The formula for Hooke's law is:
F = -kx
where F is the force exerted by the spring, k is the spring constant, and x is the displacement from the equilibrium position.
Given that the spring constant is 500 N/m and the displacement is 0.07 m, we can plug these values into the formula to calculate the force exerted by the spring:
F = -500 * 0.07
F = -35 N
Since the block moves past the equilibrium position, the friction force should be in the opposite direction to the displacement. Therefore, the force of friction that does work on the block is 35 N.