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How fast does 80 kg fall in seconds under gravity. a = 9.8ms^-2 d = 1 metre d / a = 0.10ms^-1 is this right ?  

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The acceleration due to gravity is `9.8ms^(-2)` and the mass has no effect on the velocity.

Assuming the inital velocity is 0, the velocity increases at a rate of `9.8ms^(-2)` .

So by 10 seconds the velocity is `10s` x `9.8ms^(-2)` = `98ms^(-1)`

And by 20 seconds, `196ms^(-1)`

The velocity increases linearly with time, the distance increases linearly with squared time. The formula for the distance is `t = 9.8/2 s^2`

The object takes `sqrt(2/9.8) s = 0.45s` to travel ```t=1` metre

and the speed at that point is `9.8ms^(-2)` x `0.45s` = `4.4ms^(-1)`

The average speed from 0 to 1 metre is `4.4/2 = 2.2ms^(-1)`

Check: `0.45s` x `2.2ms^(-1)` = 1 metre

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