# Impulse and momentum problem, I need help

1. Oct 7, 2013

### bchat112000

A model rocket is constructed with a motor that can provide a total impulse of 27.5 N · s. The mass of the rocket is 0.173 kg. What is the speed that this rocket achieves when launched from rest? Neglect the effects of gravity and air resistance.

i know that the equation is p=mv (vector based)

0.173*v =27.5N so how do i find velocity...

2. Oct 7, 2013

### Staff: Mentor

Hi bchat112000. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

0.173 * v = 27.5 N·s

That's one equation with one unknown. Are you able to isolate that v pronumeral to one side by itself?

Last edited by a moderator: May 6, 2017
3. Oct 7, 2013

### bchat112000

yes by multiplying by both sides???

4. Oct 7, 2013

### bchat112000

I love this forum by the way, thx for helping people

5. Oct 7, 2013

6. Oct 8, 2013

### bchat112000

i got 4.75
0.173 times 27.5n

7. Oct 8, 2013

### bchat112000

ok i plugged the formula ..initial v is 0 final v is 27.5 the mass is 0.173
0+27.5=0.173 This is the formula
27.5Ns/0.173kg=159

8. Oct 9, 2013

### Staff: Mentor

An equals sign requires what is on one side to equal what is on the other.

That looks better.

Speed requires both a magnitude and units

The correct answer is 159 m/sec