Posted by **brandon** on Thursday, June 10, 2010 at 9:49pm.

Superguy is flying at treetop level near Paris when he sees the Eiffel Tower elevator start to fall (the cable snapped). His x-ray vision tells him Lois LaTour is inside. If Superguy is 1.00 km away from the tower, and the elevator falls from a height of 122.5 m, how long does Superguy have to save Lois, and what must be his average speed?

A) 3.00 s, 333 m/s

B) 5.00 s, 200 m/s

C) 7.00 s, 143 m/s

D) 9.00 s, 111 m/s

E) 10.0 s, 96.0 m/s

- physics -
**drwls**, Thursday, June 10, 2010 at 10:05pm
Have you calculated how long it takes the elevator to free fall 122.5 m? That would be a good way to start.

Once you have calculated that time T, the speed required is easy: 1000m/T

One of the choices fits perfectly

- physics -
**brandon**, Thursday, June 10, 2010 at 10:50pm
I am really not good at physics. How would I go about finding how long it takes the elevator to fall?

Is it going to have something to do with 9.8m/s?

- physics -
**drwls**, Friday, June 11, 2010 at 12:06am
H = (1/2)g T^2, so

T = sqrt(2H/g) is the time to fall

yes, it has something to do with g.

People aren't "good at physics" until they try solving the problems.

- physics -
**A**, Sunday, January 27, 2013 at 8:27am
H=1/2gt^2

t=sqrt(2h/g)

=sqrt(2*240/9.8)

=6.99sec

speed=d/t

=1000/7

=142.8m/s

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