Momentum and Speed Lab
Name:______
Date:______
Objective: By firing a projectile into a container and measuring the distance the container slides, it is possible to find the projectile initial momentum and velocity.
Overview:
1) Find the projectile’s initial momentum and speed.
2) Check the projectile’s initial speed by firing it off of a level surface.
3) Calculate the cannon’s recoil speed.
Procedure:
Part 1: Finding the projectiles initial speed.
To find the projectiles initial speed you may choose a few different methods. The easiest would be through an energy analysis where you can calculate the speed of the box and projectile upon impact:
DKE = F x d
or
½MVf2 – ½MVI2 = Fk x d
Where Vf = 0 and Vi = the initial velocity of both the projectile and the box at impact and M is the mass of the projectile and box.
The projectile’s initial speed, right before it hits the box may be then found by using the conservation of momentum for before and after the projectile and box collision.
Write the conservation of momentum equation for right before and after the projectile strikes the box.
Step 1: Finding Fk, M, and d .
Draw the free body diagram while the box is sliding:
Use a spring scale and pull on the box (with the projectile in it) with a constant horizontal force. This will be equivalent to the net force or Fk on the box while it is sliding.
Force form scale (F):______N
Weigh the box with the projectile in it. This will be the total mass of the box while it slides.
Mass of system (M):______kg
Step 2: Fire the projectile into the box to measure the displacement.
Place your projectile in the cannon. Aim the cannon toward the opening of the box. Pull back on sling 20 cm and then fire the projectile into the box. Measure how far the box slides. This will be your distance from the work equation.
Distance box slides (d): Do this three times and take the average
m / m / m / Ave:Step 3: Calculate the velocity after impact.
Now you have all the information you need to calculate the velocity right after impact: Calculate the velocity: (Note: This is not the projectiles initial velocity leaving the cannon!!!!!!)
Using the conservation of momentum equation, find the projectiles initial velocity before striking the box. You have just found the velocity of the box right after the collision. Now your are finding the velocity right before the collision.
GOOD JOB!!!!!
Part 2: Check your results using kinematics:
Do this in the hallway!!!!!
Place the cannon on top of a stool. Pull back on the sling 20 cm and fire the cannon, then measure how far the projectile goes. If you know the height an object is fired form and the distance it travels, it is possible to calculate its initial velocity:
Measure height of cannon from the floor:______m
Distance projectile traveled:______m
-(Height) = ½(9.8m/s2)t2
Use this equation to calculate time the projectile is in the air. Next, use this time to calculate the horizontal velocity.
Flight time:______(s)
V = Distance projectile traveled / flight time
V = ______m/s
Compare this velocity to the velocity you found using the energy and momentum equation.
Part 3: Calculate the recoil speed of the cannon:
Vcannon= - (mprojectile/mcannon)Vprojectile
Weigh the cannon:______kg
Vcannon :______m/s
Concept Questions:
1) Nike uses air sacks in the heals of its shoes. Use the impulse theorem to explain why they chose to implement this design.
2) Two basketballs hit off of your head. The first one sticks and the second one rebounds. If both situations happen over the same period of time, which would hurt more and why?
4) Relative to momentum, why are our knees so important?
5) Mr T. and the New Brighton High School are in outer space and connected by a rope. Mr.T begins to pull on the rope for 10 seconds. Is momentum conserved if Mr T and the building make up the system? Why?
6) A meteor falls from space to the earth. How would you describe this situation in term of momentum being conserved?
7) In the early 1900, Robert Goddard proposed sending a man to the moon, however people thought it was impossible because once the spaceship left the earth it would have nothing to push off of. Why is this not true?