predict the reading of the spring balance when the wooden block is pulled on the sandpaper. Explain your answer.

* if the spring force is greater than the maximum of the static friction force,  

               Fe = m (a + μ_k g)

* If the elastic force is less than or equal to the static friction force, the result is with static friction coefficient

              Fe =μ_s m g

Explanation:

For this exercise we must apply Newton's second law to the system

X axis

         Fe -fr = m a

         Fe = m a + fr

Y axis  

        N-W = 0

        N = W = mg

the roe force is given by

        fr = μ N

        fr = μ mg

we substitute

      Fe = m a + μ m g

      Ee = m (a + μ g)

Let's analyze the solution. We have several possibilities

* if the spring force is greater than the maximum of the static friction force, the system acquires an acceleration and the result is with the kinetic friction coefficient

               Fe = m (a + μ_k g)

* If the elastic force is less than or equal to the static friction force, the result is with static friction coefficient

              Fe =μ_s m g

false br

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.