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# Physics motion question? watch

1. A helicopter is rising vertically at 10m/s when a wheel falls off. The wheel hits the ground 8 seconds later. Calculate at what height the helicopter was flying when the wheel came off.

I've been trying to do this for about an hour now, if someone could at least point me in right direction I'd be really grateful
3. (Original post by jackien1)
I'm not sure
How did you get to 394m?
4. s-?
u-10
v-
a-9.81
t-8

s = ut + 1/2 at2

but i assumed that a = 9.81 and i'm not sure if that's correct.

You don't have the answer scheme? Maybe you could ask a friend for their answer to see what it is then work backwards?
5. (Original post by jackien1)
s-?
u-10
v-
a-9.81
t-8

s = ut + 1/2 at2

but i assumed that a = 9.81 and i'm not sure if that's correct.

You don't have the answer scheme? Maybe you could ask a friend for their answer to see what it is then work backwards?
Ahh thank you! This sounds right, except we got given that g = 10 m/s (rounded up) so a = 10, but the method I guess is right so thanks.
Ahh thank you! This sounds right, except we got given that g = 10 m/s (rounded up) so a = 10, but the method I guess is right so thanks.
Ah, you got g = 10, then that should be fine. You're welcome! (Hopefully the answer is correct.)
7. (Original post by jackien1)
Ah, you got g = 10, then that should be fine. You're welcome! (Hopefully the answer is correct.)
again, thank you
8. Be careful of directions in this question. The helicopter (and hence wheel) are initially rising vertically upwards, but the wheel then accelerates downwards when it falls off. So defining downwards as positive, u = -10 ms^-1 and a = 10 ms^-2. Or defining upwards as positive then u = 10 ms^-2 and a = -10ms^-2 (note that if you define upwards as positive you should expect a negative displacement, so do not worry if you get so).

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Updated: September 14, 2015
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