The average speed is the distance (a scalar quantity) per time ratio. Speed is ignorant of direction. On the other hand, velocity is a vector quantity; it is direction-aware. Velocity is the rate at which the position changes.
I think it’s D but i’m not too sure
The gravitational force between the spheres is

where <em>G</em> = 6.674 x 10⁻¹¹ N m²/kg².
The weight of the lighter sphere is

where <em>g</em> = 9.80 m/s².
The ratio between the two forces is then

According to Newton's second law, the resultant of the forces acting on the box is equal to the product between its mass and its acceleration:

(1)
we are only concerned about the horizontal direction, so there are only two forces acting on the box in this direction:
- the horizontal component of the force exerted by the rope, which is equal to

- the frictional force, acting in the opposite direction, which is equal to

By applying Newton's law (1), we can calculate the acceleration of the box:

Use the formular d = v x t
d = 2m
v= 100m/s
t= d / v
= 2 / 100
= 0.02sec