# Finding Terminal Velocity given Mass and magnitude

1. Mar 24, 2013

### Matt_h

I'm in physics 1 in college and reviewing for an up comming exam, ran into this problem and cant seem to figure out how to solve it.

A 70 kg skydiver experiences a drag force as a function of velocity (in m/s), opposite the direction of motion, whose magnitude is given

Fd(v)=0.19v^2

What is the skydiver's terminal velocity?

Any help would be appreciated!

2. Mar 24, 2013

### TSny

Hi, Matt h. Welcome to PF!

The rules here require you to show some attempt at a solution before receiving help. So, how do you think you could get started on this problem? What physics principles or laws are relevant?

3. Mar 24, 2013

### Matt_h

Oh, ok

Using F=ma i found out that the force due to gravity is
70kg*9.81m/s^2=686.7N

Would i then just plug this force into the magnitude equation above to find the velocity?

After plugging it in i got 60.1 m/s

Does that sound about right?

4. Mar 24, 2013

### TSny

Yes, that looks very good. Do you see why you should set the magnitudes of the two forces equal to each other?

5. Mar 24, 2013

### Matt_h

I'm not sure that i do, do you mind explaining it?

6. Mar 24, 2013

### TSny

Newton's 2nd law: Fnet = ma

For an object moving at terminal velocity, what is the value of the acceleration a?

7. Mar 24, 2013

### Matt_h

Acceleration would be 0, right?

or no acceleration?

8. Mar 24, 2013

### TSny

Yes. So,...

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