# Homework Help: Kinematics Question

1. Jan 13, 2006

### BigCountry

Good Morning,

Just checking my work, your help would be much appreciated.

A bullet is fired vertically into the air at a speed of 512 m/s.

a) To what maximum height will the bullet does the bullet go?

b) How much time passes before the bullet stops rising?

c) What is the velocity of the bullet after 60 seconds?

a)

Vi = 0, Vf = 512, g = -9.8, find d

512^2 = 2(-9.8)d
262144 = (-19.6)d
262144/(-19.6) = d
13375 m = d

b)

Vi = 0, Vf = 512, g = -9.8, find t

Vf = Vi + at
512 = 0 + (-9.8)t
512/(-9.8) = t
52.24 Secs = t

c)

Vi = 0, g = -9.8, t = 8, find Vf

Vf = Vi + at
Vf = 9.8 * 8
Vf = 78.4 or 78 m/s^2

Thank You

2. Jan 13, 2006

### Galileo

All correct.
Better not use t=8s in c), but the more accurate 7.76s. Makes a difference of 2m, but who's counting.

3. Jan 13, 2006

### Staff: Mentor

I'd say that Vi = 512 m/s, Vf = 0. (This way you won't have to ignore any strange minus signs. ) Otherwise, looks good.

Again: Vi = 512 m/s, Vf = 0. Otherwise, looks good.

Huh? t = 60 s, not 8. (Again: Vi = 512 m/s) Note: Signs count!

(Note: Now I see what you did for question c: You started from the top. Good! But take Galileo's advice about accuracy. Note that the velocity is negative.)

Last edited: Jan 13, 2006
4. Jan 13, 2006

### BigCountry

Thanks Galileo!

Much appreciated!