# Homework Help: Calculate the total momentum after the collision

1. Oct 2, 2005

### daewoo

Hey guys, i'm stuck on this momentum question, i think I have an idea but have no way in proving it.

(here is part c to the question)
Calculate the total momentum after the collision. Compare this value to the total momentum before the collision. If these values differ, some likely causes of error were?

Mass(1)= 0.55kg, Mass(2)=0.55Kg, V1 =(0.79m/s East), V2= (0m/s)
V1 prime = (0.366m/s, 51 degrees N of E), and V2 Prime = (0.61m/s, 21 degrees S of E)

the prime means the change in velocity after a "collision" i first thought of using (m1v1 + m2v2) =(m1v1(prime) + m2v2(prime)) but the degrees and direction are confusing me, Unless i should use vector addition to add the angles.

Any ideas?

2. Oct 2, 2005

### Pyrrhus

Momentum is a vector quantity, so yes, Vector addition.

3. Oct 2, 2005

### daewoo

thought so, but how would I start it off? would i find the momentums of the primes then draw it? finding the x and y componets?

4. Oct 2, 2005

### Pyrrhus

Yes.

$$Info$$
$$|\vec{v}_{1}|= 0.366 m/s$$
$$|\vec{v}_{2}|= 0.61 m/s$$
$$\theta_{1} = 51^{o}$$
$$\theta_{2} = 21^{o}$$

$$\vec{v}_{1} = |\vec{v}_{1}| \cos \theta_{1} \vec{i} + |\vec{v}_{1}| \sin \theta_{1} \vec{j}$$

$$\vec{v}_{2} = |\vec{v}_{2}| \cos \theta_{2} \vec{i} - |\vec{v}_{2}| \sin \theta_{2} \vec{j}$$

$$\vec{v}_{R} = \vec{v}_{1} + \vec{v}_{2}$$

$$\vec{p}_{total} = m \vec{v}_{R}$$

Last edited: Oct 2, 2005