# physics

posted by on .

An object falls from height h from rest and travels 0.45h in the last 1.00 s.
(a) Find the time of its fall.
(b) Find the height of its fall.

I've tried multiple times but I cannot get the correct answer.

• physics - ,

I assume that is .45m in the last second.

WEll, its average veloicty was .45m/s. Knowing its acceleration,

vf=vi+at in the last second, but avg velocity= vf+vi)/2 or

2 avgvel=vf+ vi or vi=2avgv-vf

vf=2avgv-vf+g
2vf=2avgv+g
vf=avgv + g/2 so solve for vf
Finally,
v=gtimefall solve for time of fall
h=1/2 g t^2

• physics - ,

bobpursley,

No, the question actually says it travels 0.45h in the last second. So its 45% of the total height I believe. Unless it was a typo the average velocity is unknown. The only information known is its initial velocity (at the top of the fall, not only the last second) and the distance (0.45h) it falls in the last second.

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