Active Figure 6.10 Perfectly Inelastic Collisions
In the animation below, two particles experience an inelastic collision in one dimension.
Instructions: Use the four sliders to select values for initial velocity and mass; then click start to play the animation. Assume that all quantities have SI units.
Background
In a perfectly inelastic collision, the colliding objects stick together or become entangled after the collision. Thus, conservation of momentum gives the following equation.
m1v1i + m2v2i = (m1 + m2)vf
Solve this for the final velocity vf:
vf =   (1)
Explore
First, adjust the sliders so that m1 = m2 = 11 kg. Then set v1i = 5 m/s, and v2i = -5 m/s. Before you click start, let's use Equation 1 to make a prediction:
vf = Enter an exact number.
1 m/s
Now click start to see if your prediction agrees with the animation.
Next, predict what will happen if m1 = m2 = 4 kg, v1i = 13 m/s and v2i = -13 m/s.
vf = Enter an exact number.
2 m/s
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Now click start to see if you prediction agrees with the animation.
Sometimes, it pays to be careful with equations such as Equation (1). Consider one more case: m1 = m2 = 4 kg, v1i = +13 m/s and v2i = +13 m/s. This the same as the above case except that both velocities are positive. Take a minute to make a prediction, then click start to see if you were right.
Remarks
Did you predict 13 m/s? Obviously, this cannot be correct (play the animation to verify). The only safeguard that comes with Equation (1) is your own intuition!
Exercise 6.10
Suppose m1 = 8.77 kg, m2 = 10.79 kg and vf = 5.95 m/s. If v1i = 10.9 m/s, what was v2i?
v2i = Enter a number.
3 m/s
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