Answer:
500 N
Explanation:
Since the work done on the spring W = Fx where F = force applied and x = compression length = 0.170 m (since the spring will be compressed its full length when the force is applied)
Since W = 85.0 J and we need to find F,
F = W/x
= 85.0 J/0.170 m
= 500 N
So, the magnitude of force must you apply to hold the platform stationary at the final distance given above is 500 N.
The mass of the box would be 30!
It takes greater force to accelerate an object that has more mass. But the gravitational force between the Earth and an object is greater when the object hass more mass. It works out just right to make any object with any mass accelerate at the same rate.