# Homework Help: Impulse and Momentum Q!

1. Dec 9, 2009

### ReMa

I have two questions regarding this, any help would be GREAT!

1st Problem:

1. The problem statement, all variables and given/known data

A conveyor belt lifts 1000kg of rocks per minute a vertical distance of 10m. The rocks are at rest at the bottom of the belt and are ejected at 5 m/s. The power supplied to this machine is:

A) 1000W
B) 1260W
C) 1630W
D) 1840W
E) 2100 W

2. Relevant equations

P=Fv

p=mv
$$\sum$$F$$\Delta$$T=m(vf-vo)

3. The attempt at a solution

vo = 0m/s
vf = 5m/s

1000kg/min = 16.67kg/s

sumF$$\Delta$$T=m(vf-vo)
sumF=m(vf-vo)/$$\Delta$$T
sumF=m(vf)-m(vo)/$$\Delta$$T

since vo = 0/ms

sumF=m(vf)/$$\Delta$$T
sumF=m/$$\Delta$$T (vf)

subbing in values...

m/dT = 16.67kg/s

F = (16.67)(5) = 83.35N

and now for Power...
P = Fv
P = 83.35(5) = 416.75W

Now, I know i've done something wrong, especially as I haven't accounted for height. I feel like I am EXTREMELY off with attempting to solve this so i'd appreciate any help.

2nd Problem:

1. The problem statement, all variables and given/known data

Water runs out of a horizontal pipe at the rate of 120kg/min. It falls 3.20m to the ground. Assuming the water doesn't splash up, what average vertical force does it exert on the ground?

2. Relevant equations

P=Fv

p=mv
sumF$$\Delta$$T=m(vf-vo)

3. The attempt at a solution

SOLVED THIS ONE - if anyone else needs the solution though let me know and i'll post it.
Still need help on the first though... workin' on it however.

Last edited: Dec 9, 2009
2. Dec 9, 2009

### RoyalCat

For the first problem, ignore the forces within the machine. Ask yourself what happens to the rocks every second (Think energy rather than momentum)