Question

Choose from the following to answer questions 1-4.

Answer choices:  A. at rest   B. moving backwards   C. moving forward

                            D. 0          E.  < 0.2 m/s         F. 0.2 m/s         G. > 0.2 m/s

If wagon 1, initially moving in the forward direction with velocity v_1i = 0.2 m/s, collides with wagon 2, mass m₂,  which is initially at rest, v_2i = 0,  then

1. If the collision is elastic and the wagons have equal mass,  m₁ = m₂ , then after the collision

wagon 1 is  _____ with v_1f  _____, and wagon 2 is  ______ with v_2f  ______.

2. If the collision is elastic and wagon 1 is more massive,  m₁ = 2*m₂ , then after the collision

wagon 1 is _____ with v_1f  _____, and wagon 2 is ______ with v_2f  ______.

3. If the collision is elastic and wagon 2 is more massive,  m₂ = 2*m₁ , then after the collision

wagon 1 is _____ with v_1f  _____, and wagon 2 is ______ with v_2f  ______.

4. If the collision is perfectly inelastic, then whatever the masses of the wagons, after the collision

wagon 1 is _____ with v_1f  _____, and wagon 2 is ______ with v_2f  ______.

Please examine the graphs and figure out what is happening.  Fill in the blanks with these choices.

A. at rest   B. moving toward the left   C. moving toward the right   D. 0   E. 0.2 m/s

F. Professor Schnal   G. Cart 1   H. placed it there at rest.  J. gave, or is giving, it a push.   

At time 1.5 seconds, Cart 1 is ______ with a speed of ______ m/s because ____  _____.

At time 1.5 seconds, Cart 2 is ________ with a speed of _______m/s because ____ _____.

By time 2.1 seconds, Cart 2 begins  _______   because _____     _____.

By time 2.5 seconds, the collision is pretty much over, and Cart 1 is ______ with a speed of _______ m/s, and Cart 2is _______ with a speed of _________ m/s.

                 

What does it mean when the red and blue lines on the position graph cross at 2.1 seconds?

1. The carts collide
2. The red cart ghosts through the blue cart somehow.
3. Nothing: the red cart just happens to be as far from the left detector as the blue cart is from the right detector.

Cart 2  in elastic.cmbl  is clearly experiencing substantial friction.  How can you tell?

1. Cart 2 maintains constant velocity after the collision.
2. Cart 2 decelerates at a rate of about 0.5 m/s/s after the collision.
3. The blue line crosses the red line at time 2.1 seconds.

Because of cart 2’s friction, let’s take the v_f data as soon as possible after the collision.

For elastic.cmbl, take initial velocity data at t = 1.6 s, or t = 1.7 s, or t = 1.8 s. (It’s the same.)

For elastic.cmbl, take final velocity data at t = 2.5 s.  (You could argue that that’s a little premature, that there is some settling down after that time, but  it’s best to take it before friction has a chance to substantially affect the results.  Also it’s nearly identical to the data at t = 2.75 s, after the funny wiggle from t = 2.5 s to t = 2.75 s settles down.)

Answer 1

If the collision is elastic, and the wagons have equal mass m₁ = m₂, then after the collision wagon 1 is (A) at rest with v_1f(D) 0, and wagon 2 is (C) moving forward with v_2f(G) > 0.2 m / s.

If the collision is elastic, and wagon 1 is more massive : m₁ = 2m₂, then after the collision wagon 1 is (C) moving forward with v_1f(E) < 0.2 m / s, and wagon 2 is (C) moving forward with v_2f(G) > 0.2 m / s.

If the collision is elastic, and wagon 1 is more massive : m₁ = 2m₂, then after the collision wagon 1 is (B) moving backward with v_1f(E) < 0.2 m / s, and wagon 2 is (C) moving forward with v_2f(E) < 0.2 m / s.

Finally, for completely inelastic collision, some energy is lost in form of heat or other energies. Hence, both the wagons will move forward with a velocity less than 0.2 m / s, after sticking together.

Hence, if the collision is perfectly inelastic, then whatever the masses of the wagons, after the collision wagon 1 is (C) moving forward with v_1f(E) < 0.2 m / s, and wagon 2 is (C) moving forward with v_2f(E) < 0.2 m / s.