PhysicsLAB Lab
Ballistic Pendulum: Muzzle Velocity

In this experiment we will use a ballistic pendulum to determine the initial horizontal launch velocity of a brass ball. The first method will use horizontal projectile motion while the second method will use conservation of momentum and conservation of energy. At NO time during the experiment are you to adjust the spring gun's tension.
 
In the first part of the experiment you will carefully displace the pendulum so that you can use the spring gun to project the brass ball as a horizontal projectile. By measuring the ball's range and height of release you will be able to calculate the ball's flight time and its muzzle velocity.
 
 
In the second part of the experiment you will fire the brass ball from the spring gun into the pendulum which will swing up and be caught at its highest displacement. This inelastic collision initially conserves momentum while the pendulum's swing conserves energy. You will then be able to once again calculate the ball's release velocity. A percent difference between the two values for the ball's release velocity will conclude your calculations.
 
 
In addition to the ballistic pendulum, you will need the following equipment:
 
  • 1 triple beam balance
  • 1 meter stick
  • carbon paper
  • plumb line
  • target paper
 
 
Part I
 
As shown in the top picture above, carefully secure the pendulum out of the path of the ball. Test fire the spring gun and note where the brass ball strikes the floor then place your target paper and carbon paper near the anticipated point of contact. Use a plumb line to record the location of the edge of the table on the floor. After firing the gun more five times, measure and record each of the ball's impact positions. Remember to always make sure that the base of the pendulum is flush with the edge of the desk before each firing. When you are finished, fold up your target paper and place the names of your group members on the outside. This paper must be turned in to your instructor.
 
  range
trial (m)
1
2
3
4
5
What was the ball's average range (in meters)? 

Through what vertical height did the ball fall (in meters)? 

How much time did the ball spend in the air (in seconds)? Remember to show your calculations on this lab sheet. 

What was the brass ball's initial horizontal velocity when first released from the spring gun (in m/sec)? Remember to show your calculations on this lab sheet. 

 
 
 
 
Part II
 
Mass the ball and then, as shown in the picture below, carefully move the pendulum so that it is now directly in the ball's line of fire. Measure and record the height of the screw on the side of the pendulum's cup. You will now fire the ball five times into the catcher, each time recording the height that the pendulum's cup recoils.
 
equilibrum position recoil height
 
What was the mass of the brass ball (in kg)? 

How high was the pendulum cup's screw while the pendulum was hanging it its equilibrium position (in cm)? 

  recoil height Δ height
trial (cm) (cm)
1
2
3
4
5
What was the ball and catcher's average change in height (in meters)? 

Find out from your instructor the mass of the pendulum and its catcher (in kg). 

Use conservation of energy principles to determine the initial KE (in J) of the ball and catcher immediately after impact. Remember to show your calculations on this lab sheet. 

Calculate the velocity of the ball and the pendulum catcher immediately after the ball's impact. Remember to show your calculations on this lab sheet. 

Use conservation of momentum to determine the initial horizontal velocity of the brass ball when first released from the spring gun. Remember to show your calculations on this lab sheet. 

 
 
 
 
Analysis
 
Compare your two values for the ball's muzzle velocity from Part I and Part II by performing a percent difference. Remember to show your calculations on this lab sheet. 

Which method do you think had the more accurate results? Support your choice.
 



When you have completed this lab, make sure that you submit your results online as well as turn in your calculations and target paper. Names are important!


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