PhysicsLAB Lab
Inelastic Collision - Velocity of a Softball

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This lab is a ballistic pendulum analogy. Its purpose is to determine the velocity of a softball using equations from the law of conservation of momentum and work-energy relationships.
  • cardboard box
  • packing material (plastic bags and paper)
  • softball
  • meter stick
  • spring scale
  • triple beam balance
Procedure and Data

1. Loosely pack a cardboard box with packing material so that a softball thrown into the box will remain trapped - you do not want the ball to "bounce back out!"
2. Measure and record the mass of the softball and then the mass of the packed box.
mass of softball (kg) 

mass of packed box (kg) 

total mass of packed box and softball (kg) 

3. Place the box on a smooth surface and mark its starting position.
4. Throw (do not roll) the softball into the box - be careful to not tip the box over or cause it to spin, you only need to throw the ball fast enough to move the box 10-30 centimeters in a straight line.
5. Measure and record the distance the box moved.
distance box traveled (m) 

6. Measure the force of friction by pulling the box (with the ball still trapped inside) at a constant speed across the same section of floor. Remember that the spring scale MUST remain parallel to the floor.
frictional force (N) 

Calculations and Analysis
1. How much work, in joules, was done on the box by friction as the box, packing and softball slid to a stop after the collision? 

Enter your data for friction and distance traveled in the EXCEL spreadsheet, work.xls, to verify your calculations. Then complete the following statement: 
The work done by a force F acting through a distance s is determined graphically as the ____  of the graph.

2. Which forces would belong on a freebody diagram of the box as it slides to a stop? (assume that it is moving towards the right)
3. What average acceleration, in m/sec2, did the box experience? 

4. How fast, in m/sec, was the box, packing and softball moving immediately following the collision? 

5. What impulse, in N sec, did the softball deliver to the box and packing material? 

6. By Newton's third law, the impulse delivered to the box and packing material equals the impulse received by the ball. Using this information, calculate the initial velocity, in m/sec, of the softball. 

7. Devise a follow-up experiment that could be conducted to verify the value for the velocity calculated in question #6. 

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