- #1

cassie123

- 15

- 0

## Homework Statement

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A 2.0 kg ball moving with a speed of 3.0 m/s hits, elastically, an

identical stationary ball as shown. If the first ball moves away

with angle 30° to the original path, determine:

a. the speed of the first ball after the collision.

b. the speed and direction of the second ball after the

collision.

## Homework Equations

px: m1v1=m1v'1cosΘ1+m2v'2cosΘ2

py: 0=m1v'1sinΘ1+m2v'2sinΘ2

KE: 1/2m1v1^2=1/2m1v'1+1/2m2v'2

where I am using 1 and 2 to denote the first and second balls. and the "prime's" denoting final speed.

Θ1=30°

Since the balls have identical mass, I believe mass cancels out of the above equations.

## The Attempt at a Solution

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What I tried to do was to find the components of the vectors of final motion, use the conservation of momentum and kinetic energy to create three equations to solve for the three unknowns (Θ2, v'1, v'2).

I canceled the mass out of all three equations, rearranged so that the Θ2 terms are on the same side of the momentum equations. I then squared the momentum equations and added them so that I could use the identity cos^2Θ+sin^2Θ=1 to get rid of the Θ2 terms and only have to solve for v'1 and v'2 using the KE equation and the added momentum equations. This is where I am getting stuck with the algebra:

(v1-v'1cos(30))^2+(-v'1sin(30))^2=(v'2)^2

and v'2=(v1)^2-(v'1)^2

so, subbing in for v'2:

(v1-v'1cos(30))^2+(-v'1sin(30))^2=(v1)^2-(v'1)^2

and at this point I should be able to solve for v'1, but i can't figure it out