an object is falling freely from rest of height of 65m above the ground what is the height of the object from the ground in meter when it reaches velocity of 20m/s?

To find the height of the object from the ground when it reaches a velocity of 20 m/s, we can use the equations of motion for an object falling freely under gravity.

The equation we need is:

v^2 = u^2 + 2as

where:
v = final velocity (20 m/s)
u = initial velocity (0 m/s, as the object starts from rest)
a = acceleration due to gravity (-9.8 m/s^2, assuming downward direction)
s = displacement

We want to find the displacement, which represents the height from the ground. We know that the object is falling, so the acceleration due to gravity is negative (-9.8 m/s^2). The initial velocity is zero because the object starts from rest.

Substituting the given values into the equation:

(20 m/s)^2 = 0^2 + 2 * (-9.8 m/s^2) * s

400 m^2/s^2 = -19.6 m/s^2 * s

Now, solve for s (displacement):

s = 400 m^2/s^2 / (-19.6 m/s^2)

s ≈ -20.41 m

The negative sign indicates that the displacement is in the downward direction. However, since we are interested in the height from the ground, we take the magnitude of the displacement by considering the absolute value.

So, the height of the object from the ground when it reaches a velocity of 20 m/s is approximately 20.41 meters.

v = 9.8t, so it takes 20/9.8 = 2.04 seconds to achieve that speed.

Since h = 65-4.9t^2,
plug in 2.04 to get h at that time.