Minimum work for 65 kg student climbing 8.0 m stairway in 12 s

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brentwoodbc
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Homework Statement



What is the minimum work done when a 65 kg student climbs an 8.0 m-high stairway in 12 s?




The Attempt at a Solution


v=d/t
v=8/12
v=2/3

v = v2+v1 over 2
2/3 = v2+0 over 2
v2 = 2x[2/3]
v2=4/3

w=deltaEk
w=.5x65x[4/3]^2 - .5x65x0
w = 57 j ?

answer is 5100 j
 
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Discussion



Hint :work is force times distance. So the time taken does not matter at all.
 


brentwoodbc said:
I know
w=fd
f=ma
f=65x9.8
f=5096

but that doesn't have time or distance.

It seems you got the answer!
The minimum work needed would be done by a force acting upward, in the opposite direction of the weight. Its magnitude would have to be greater than the weight, so >65 kg*9.8m/s^2 as you did.
You wrote w=fd, where w is the work, f is the force and d is the distance. Then you said that the formula doesn't have a distance?
Well you've done it :)
 


fluidistic said:
It seems you got the answer!
The minimum work needed would be done by a force acting upward, in the opposite direction of the weight. Its magnitude would have to be greater than the weight, so >65 kg*9.8m/s^2 as you did.
You wrote w=fd, where w is the work, f is the force and d is the distance. Then you said that the formula doesn't have a distance?
Well you've done it :)

haha, i know what I typed wasnt actually what I did.