What is the velocity after 8 seconds as it falls freely from rest?

Answer 1

Ignoring air resistance:

acceleration due to gravity is approx 9.81 m/s²

Using Newton's equation of motion:

v = u + at

where:

• v = final velocity (to find)
• u = initial velocity = 0 m/s as it was at rest
• a = g - acceleration due to gravity (in a downward direction)
• t = 8 s

v = 0 + g × 8 = 8g (downwards)

Taking g as 9.81 m/s² this makes the final velocity v ≈ 8 s × 9.81 m/s² = 78.48 m/s ≈ 78.5 m/s

Answer 2

The final velocity will be -78.4 m/s. The negative sign means the motion is downward.

Use equation: vf = vi + g x t, where vf is final velocity, vi is initial velocity, g is acceleration due to gravity, and t is time interval.

Known

vi = 0 m/s

g = -9.8 m/s/s = -9.8 m/s2

t = 8 s

Unknown

vf

Solution

Plug in the known values and solve.

vf = 0 + (-9.8 m/s/s) x 8 s

vf = -78.4 m/s

Answer 3

Approx 78 metres per second.