- #1

cleverfield

- 12

- 0

## Homework Statement

The terminal velocity of a 3×10−5kg raindrop is about 5m/s . Assuming a drag force , and Drag Force = -bv

1. Assuming a drag force determine the value of the constant .

2. Assuming a drag force determine the time required for such a drop, starting from rest, to reach 63% of terminal velocity.

## The Attempt at a Solution

I solved Q1 with an answer of b=6*10^-5 kg/s

for #2. I used Vfinal = Vinit + at

Equation 1 = V final = 0.63 of Vterm and therefore is 3.15 m/s

V init = 0

a = ?

Time = ?

for a I used the constant b and did FBD and N2

got Fdrag - mg = ma

Work:

-(6E-5kg/s)(3.15m/s) - (3E-5kg)(9.8m/s2) = (3E-5kg)a

but that gives a = -16.1 m/s2 which doesn't make sense to me. And i dropped that number in equation 1 above.

Thanks