How Tall Was the Initial Fall in a Physics Problem?

[ryno2107]

A freely falling object requires 1.10 s to travel the last 20.0 m before it hits the ground. From what height above the ground did it fall? (Ans. in m.)

I am completely lost on modeling this problem. Please help me figure it out.

 

[Delphi51]

The model is just accelerated motion so you have the usual
V = Vi + at and d = Vi*t + .5*a*t^2 to work with.
Looks like you don't have enough info to use the first one, but the second one can be used to get the Vi - the velocity at height 20 m.
That's a good start. Then you can use the first equation to found out when the velocity was zero.

 

[tomcue]

I would approach this problem by using the equation for free fall, which is d = 1/2 * g * t^2, where d is the distance traveled, g is the acceleration due to gravity (9.8 m/s^2), and t is the time.

In this case, we know that the object traveled 20.0 m in 1.10 s, so we can plug those values into the equation and solve for the initial height (h) of the object before it fell:

20.0 m = 1/2 * 9.8 m/s^2 * (1.10 s)^2 + h

20.0 m = 5.39 m + h

h = 20.0 m - 5.39 m

h = 14.61 m

Therefore, the object fell from a height of 14.61 meters above the ground. I hope this helps you understand the problem better.