# Classic Hit and Stick momentum?

NoobeAtPhysics

## Homework Statement

Three balls of clay have masses m1 = 106 g, m2 = 148 g, m3 = 120 g, and speeds v1 = 1.48 m/s, v2 = 1.19 m/s, v3 = 1.85 m/s. They move in the directions: (1) at 45° from the horizontal, (2) horizontally left, and (3) vertically up. They collide simultaneously and stick together. Calculate the speed and the direction (angle) of the resulting blob of clay.

p=mv

## The Attempt at a Solution

Vx = 106 * 1.48 * cos(45) - 148 * 1.19 = -65.189882 m/s

Vy = 106*1.48sin(45) + 120*1.85 = 332.0309 m/s

V = sqrt(332.0309^2 + [-65.189882]^2) (answer?)

angle = arctan (Vy/Vx)

This isn't right is it,

Homework Helper

## Homework Statement

Three balls of clay have masses m1 = 106 g, m2 = 148 g, m3 = 120 g, and speeds v1 = 1.48 m/s, v2 = 1.19 m/s, v3 = 1.85 m/s. They move in the directions: (1) at 45° from the horizontal, (2) horizontally left, and (3) vertically up. They collide simultaneously and stick together. Calculate the speed and the direction (angle) of the resulting blob of clay.

p=mv

## The Attempt at a Solution

Vx = 106 * 1.48 * cos(45) - 148 * 1.19 = -65.189882 m/s

Vy = 106*1.48sin(45) + 120*1.85 = 332.0309 m/s

V = sqrt(332.0309^2 + [-65.189882]^2) (answer?)

angle = arctan (Vy/Vx)

This isn't right is it,
First of all we have to know the direction of the 45° ball. Is it 45° to the left or to the right?

It is not clear what you are doing in calculating vx and vy.

I suggest you write out the equations for momentum before and after the collision and then relate them. How are they related?

AM

1 person
Legaldose
No that isn't right, remember that the conservation of momentum applies, use it. Calculate the total momentum in the x direction before the collision, then it them equal to the total momentum in the x direction after the collision, then do the same for the y direction. Then you will have two equations with two unknowns, use algebra to solve for both. What you did was incorrect, you cannot find the total momentum in the x direction and set it equal to the velocity in the x direction. If in doubt, check the units.

1 person
NoobeAtPhysics
So

mv = m1 * v1 + m1*v2 + m2*v3? in the x and y directions then use trig to find speed and direction?