# Homework Help: Rock Problem Part 2

1. Jan 25, 2006

### 29 clicks

This is the second hardest question on my test, how long does it take to push a rock 10m.

50Kg rock
10 m is the distance
0.16m/s2 is the acceleration

Does anyone know which kinematics equation I should use for this problem.

2. Jan 25, 2006

### matrixx333

The four kinematic equations are:

d = vi*t + 1/2*a*t2

vf = vi + a*t

vf2 = vi2 + 2*a*d

d = vi + vf/2 *t

You want to pick the equation that has a "t" in it, and the one that has the most of your information already provided.

P.S. your initial velocity is 0 m/s, remember!

3. Jan 26, 2006

### 29 clicks

I know its the first equation since i have all the information except for t, but i'm not good at rearranging question so can you help me just a bit more. Really appreciate it.

4. Jan 26, 2006

### matrixx333

ok, so lets substitute the values for what we "know"

d = vi*t + 1/2*a*t2, which would equal:

10 = (0)*t + 1/2*(.16)*t2

we want to try and solve for t, in the first part of the equation, (0)*t, we know that equals 0, so we can get rid of that part, now our equation is:

10 = 1/2*(.16)*t2

can you take it from there?