okay, okay, okay already -- I'll take a breather on the physlets this week (maybe look at a few in class, but I won't ask you to look at any on your own). I still expect you to do some work online though and once again due on Friday, September 23.
Let us talk about inelastic collisions.
Imagine a 5 kg cart A traveling 4 m/s to the east. Imagine a second 5 kg cart moving 3 m/s to the west. Imagine that the carts collide and couple so that a train of two carts continues in one connected motion.
Answer the following questions (don't forget that momentum is a vector and that it therefore gets a sign according to its direction):
Consider a fully loaded boxcar of 130,000 kg traveling east at 2.6 m/s that overtakes a "train" of 4 coupled 30,000 kg empty boxcars already traveling east at 1.8 m/s. Assuming that momentum is conserved, what is the velocity of the resulting 5 car train?
Consider a 2500 kg sportscar traveling south on Cicero at a rate of 40 m/s. A3000 kg pickup truck traveling east on 167th is moving at 25 m/s. At about the same instant both drivers realize that the signal has failed and that a collision is imminent. The brakes on the sportscar provide 18000 Newtons of braking force vs. the street. The pickup is able to produce18000 Newtons as well. After the collision the state trooper is able to determine from skid marks that the car had braked for 60 meters and the truck for 30 meters.
Upon collision the two vehicles entangled and the pile-up proceeded towards the (approximate) south east. How fast was the pile moving? Bonus: in exactly what direction?
Tips on spring lab:
It is due tomorrow, Tuesday September 19. Turn it in. Consider the comments that I placed on the stairway lab before submitting this one.
Problems:
1. What was the spring constant for your spring?
2. Did the data you collected for the oscillating spring support the notion that mechanical energy is conserved in that process? Support your answer by comparing the elastic energy gained by the elongating spring and the gravitational potential energy lost by the descending spring.
Be sure your data is clearly and neatly evident and that your argument for or against conservation is easy to find and follow. Make sure all measurements are labeled and converted to the correct units.
This week: we'll observe some inelastic collisions. A collision is inelastic when the objects colliding are "stuck together" following the collision. Kinetic energy is NOT conserved in inelastic collisions but momentum is. I'll demonstrate a method to obtain very accurate and precise values for the speed of a cart. I will then ask you to obtain data in support of conservation of momentum for several sets of circumstances:
A primary object of assessment this time will be your ability to construct an appropriate data table to contain all these problems. Groups will number about 3 students each. You may share with your partners the measurements made in the lab (the mass of each cart and the times at which the photogates are interrupted and the distances between interruptions, but each will conduct his own analysis and be responsible for his own data and analysis [how fast each cart is moving before and after collision and how much momentum each part of the system has at each time] tables).
We will also have an assessment this week (Wednesday or Thursday). Expect data and analysis to appear for the second time, simple momentum and impulse for the first time and a third one from the past (speed and acceleration or work and energy?)