What was the splashdown speed?

[innersmile]

1. A 60 kg stuntperson runs off a cliff at 4.6 m/s and lands safely in the river 10.2 m below. What was the splashdown speed?

Homework Equations

PE = mgh
KE = (1/2)mv^2
PEi +KEi = PEf + KEf
(TMEi) = (TMEf)

The Attempt at a Solution

I really had no idea how to start this but this is what i did:
i used TMEi = TMEf where the mass would cancel out
so the equation you end up with would be
(60 kg)(9.8 m/s2)(10.2) + (1/2)(60 kg)(4.6 m/s)^2 = (1/2)(60kg)(v^2) << i don't think you have to add PEf to that because the height is zero

but i didn't get the right answer. I'm doing this for a webassign..

thanks for the help

 

[hage567]

You could try solving it using projectile motion equations, to see what answer you get.
What number did you get out of that calculation, by the way? Maybe you made an error?

 

[nrqed]

1. A 60 kg stuntperson runs off a cliff at 4.6 m/s and lands safely in the river 10.2 m below. What was the splashdown speed?

Homework Equations

PE = mgh
KE = (1/2)mv^2
PEi +KEi = PEf + KEf
(TMEi) = (TMEf)

The Attempt at a Solution

I really had no idea how to start this but this is what i did:
i used TMEi = TMEf where the mass would cancel out
so the equation you end up with would be
(60 kg)(9.8 m/s2)(10.2) + (1/2)(60 kg)(4.6 m/s)^2 = (1/2)(60kg)(v^2) << i don't think you have to add PEf to that because the height is zero

but i didn't get the right answer. I'm doing this for a webassign..

thanks for the help

You seem to have done it right. what did you get? How many sig figs did you use for your answer? webassign is picky about sig figs, you may have got the right answer but entered too many or too few sig figs (I am guessing too many)

 

[innersmile]

thanks for the help!
yeah i set it up right but i must have done the calculations wrong...
thanks though!