How to Calculate Average Acceleration in a Fall?

[Melchior25]

So here is the question I'm stuck on.

A woman is reported to have fallen 112 ft from a building, landing on a metal ventilator box, which she crushed to a depth of 24 in. She suffered only minor injuries.

Calculate the magnitude of her average acceleration while in contact with the box.

I know average accel. = (delta v) / (delta t)

I calculated the speed of the woman just before she collided with the box to be 84.664 ft/s.

Although I'm a bit lost on how to calculate the avg. acceleration because I'm not sure what equation I should use to calculate (t).

 

[Doc Al]

Try expressing delta t in terms of delta v and the distance.

(You can also take advantage of kinematic relationships that directly relate speed, distance, and acceleration.)