# Homework Help: Help on a rather simple physics question

1. Nov 18, 2013

### Fullmetalx

1. The problem statement, all variables and given/known data
Suppose you drop a feather and a steel ball of equal masses (0.014 kg) at the same time from a height of 1.5 m and you are told that the feather hits the floor 3.5 s after the steel ball. Estimate the value of the terminal velocity of the feather in air.

Estimate the feather's drag coefficient.

2. Relevant equations

v=mg/c

3. The attempt at a solution

I assumed the drag on the steel ball is negligible. So i used r=vit +.5at^2 to find the time it takes for it reach the ground. I then added 3.5s and used another kinematic equation to find the final velocity or terminal velocity. I then plugged the answer into the above equation to find c. it was wrong

2. Nov 18, 2013

### Simon Bridge

What does the v-t graph of the feather look like?
i.e. do the kinematic equations even apply to it's motion?

Consider: if the air-resistance for the steel ball can be neglected - so it never reaches it's terminal velocity - then what is the case for the feather? How long does it take the feather to reach it's terminal velocity?

3. Nov 18, 2013

### Staff: Mentor

Assume that the feather reaches its terminal velocity instantaneously. How far did it fall? How many seconds did it take to fall this distance? What was its velocity?