# Free fall Question

1. Feb 9, 2016

### derpeedoo

1. The problem statement, all variables and given/known data
While parachuting, you dropped your sun glasses at a height of 1400m and it took 15 seconds for the glasses to fall onto the ground. What is your descend speed after you dropped your sun glasses?

2. Relevant equations
Y = VoT + 1/2at^2

3. The attempt at a solution
My thought process: The glasses must have the same velocity as me when I dropped them. Therefore, its initial velocity during the free fall is my descend speed.

1400m = Vo(15s) + .5(-9.8m/s^2)(15s)^2
Vo = 20 m/s

The answer key says my descend speed is 9.8 m/s

2. Feb 9, 2016

### jbriggs444

A book that poses a problem involving parachuting without being cognizant of the fact that the terminal velocity of a pair of sunglasses is far, Far, FAR less than 100 meters per second should be discarded.

3. Feb 9, 2016

### derpeedoo

This question was on a previous physics exam. Is there anyway for me to solve this with only knowing the basics of free fall?

4. Feb 10, 2016

### haruspex

I agree with jbriggs, but in an exam you just have to put up with it. Allowing for drag on the sunglasses would lead to an even larger answer, so I think your method was as intended by the question setter. You got a sign wrong in the first equation but appear to have corrected that, so I also agree with your answer.

5. Feb 10, 2016

### Staff: Mentor

It's a typo in the answer key. They meant 19.8.