# Acceleration and Moving Objects

1. Sep 4, 2006

### Soaring Crane

A large boulder is ejected vertically upward from a volcano with an initial speed of 40.1 m/s. (Air resistance can be ignored.)

a) At what time after being ejected is the boulder moving at 19.2 m/s upward? (g = 9.80 m/s^2)
b) At what time is it moving at 19.2 m/s downward? (g = 9.80 m/s^2)
c) When is the displacement of the boulder from its initial position zero? g = 9.80 m/s^2
d) When is the velocity of the boulder zero? g = 9.80 m/s^2

I did and understand these four parts. Now the following two parts are the ones I do not understand.

e) What is the magnitude of the acceleration while the boulder is moving? (Take g = 9.80 m/s^2 for free fall acceleration)

Well, the boulder can move up or down, but is the magnitude 9.80 m/s^2 for both scenarios?

f. What is the direction, up or down, of the acceleration while the boulder is moving?

Won't the direction be down?

Thanks for any help.

2. Sep 4, 2006

### Kurdt

Staff Emeritus
Yep you have that question licked it seems.

3. Sep 4, 2006

### Gablar16

Let me try to help. For (a) I think you need something similar to V=Vo+at