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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
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
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
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