Posted by **ajo** on Saturday, October 6, 2007 at 3:50pm.

A wrecking ball is hanging at rest from a crane when suddenly the cable breaks. The time it takes for the ball to fail halfway to the ground is 1.2s. Find the time it takes for the ball to fall from rest all the way to the ground.

Can anyone give me some hints to do this?

Thanks a lot!

- physics -
**tchrwill**, Saturday, October 6, 2007 at 4:16pm
A wrecking ball is hanging at rest from a crane when suddenly the cable breaks. The time it takes for the ball to fail halfway to the ground is 1.2s. Find the time it takes for the ball to fall from rest all the way to the ground.

Can anyone give me some hints to do this?

Thanks a lot!

h/2 = Vot + 16t^

Vo = 0

h/2 = 16^2

h/2 = 32(1.2)^2 or h/2 = 46.08 ft.

h = 92.16 ft. = 16t^2

t^2 = 5.76 making t(ground) = 2.4 seconds.

- physics -
**bobpursley**, Saturday, October 6, 2007 at 6:32pm
There is a typo, ajo

h/2= 16* 1.2^2

h= 46.08

to fall the entire way is

46.08=16*t^2

solve for t.

The 16 is from the formula 1/2 a t^2, where a is 32ft/s^2

You could work this in metric...

- physics -
**ajo**, Saturday, October 6, 2007 at 7:37pm
i still don't get where did you get the 16...

- physics -
**Adrian**, Saturday, December 29, 2012 at 5:59pm
X=Vot+1/2at^2 and Vot = 0 as Vo = 0 so X=1/2at^2 but as X is only 1/2 way down drop we still have a little more consideration..

So X/2=1/2at^2 and t= 1.2s so X/2 = 7.06m

Thus Total fall distance = 14.12m and...

Using 14.24 = 1/2(9.81)(t^2) we see,

Root 2(14.24)/9.81 gives us t = 1.697s which is time for full distance fall.

- physics -
**Chris**, Saturday, October 5, 2013 at 4:41pm
I cannot believe that you would even think of using 16 ft/s^2. That is ridiculous. We use the metric system in science not the english system.

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