A force of 20N is used to lift a 600g ball fro the ground to a height of 1.8m, when it is let go.?

Question

What is the speed of the ball when it is let go?

Answer 1

A net Force will cause a mass to acclerate.
net Force = mass * acceleration

In this case, you have two forces acting on the object, the force of 20 Newtons acting upward and the force of weight caused by gravity acting downward.

If the object has a mass of 600 grams (.6 kg), then the object has a weight of about 5.95 Newtons. This force is directed downward (in what we will call the negative direction).

The net force is the sum of the two force acting on the object.
net Force = +20 newtons - 5.95 Newtons
net Force = 14.05 Newtons in the positive direction

This constant net force will cause a constant acceleration of the object in the upward direction,
F = ma
(14.05 N) = (.6 kg) * a
a = 23.42 m/s^2

From here, there are actually any number of ways to solve this problem, but I am guess the one which you will be most familiar with will be to use the kinematic equation,
d = v*t + 1/2 at^2
where v is the initial velocity, t is the time, and a is the constant acceleration.
If this object experiences this net force (cause an acceleration) for a distance of 1.8 metes, this is the value we will plut into the equation for the distance (d). We assume the object started from rest (v = 0).

(1.8 m) = 1/2 (23.42 m/s^2) * t^2
now we simply solve for the time, t,
t = sqrt (2 * (1.8 m) / (23.42 m/s^2))
t = .392 seconds

Using this formula,
v = a*t
where v is now the objects velocity after experiencing a constant acceleration for time t, we solve for the object's velocitu when releases,
v = (23.42 m/s^2) * (.392 s)
v = 9.18 m/s in the upward direction.

Answer 2

10 m/s - this is free-fall. Objects will fall at the same speed regardles of their mass.