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AP Physics C: Momentum #2.6

A block of mass m1 = 2.0 kg slides along a frictionless table with a speed of 10 m/s. Directly in front of it, and moving in the same direction, is a block of mass m2 = 4.2 kg moving at 2.8 m/s. A massless spring with spring constant k = 1100 N/m is attached to the near side of m2, as shown in Fig. 10-35. When the blocks collide, what is the maximum compression of the spring?

Solution: Based on the problem you can treat the two objects as undergoing an inelastic collision.  Where does the energy go?  It gets stored in the spring!  So the spring does work on the system.  Hold that thought, it will be important soon.

Step 1) Since we know both Vi’s and we know both masses, we can solve for the final speed of the combined mass using conservation of momentum.  Now we know Vf.

Step 2) You know both Vi’s and the combined Vf, so you can calculate the total KE before the collision and doing it again gives you after the collision.  Find the delta KE before and after the collision.

Step 3)  Where did that lost KE go?  We said it earlier.

Step 4) So the spring did work which sucked up energy.  How much?  The difference you calculated in Step 2).  Why is this important?  W=deltaKE.  Oh.  That’s why its important.  So,

W=deltaKE (<–you know this number)
.5kx^2 =deltaKE
Solve for x.




AP-C Momentum 2.7

Number 7 from the second momentum HW

AP momentum 2.7


AP-1: 2D forces review materials

A-Day: This is your quiz from Friday.  Please study and make sure you can reproduce my results.  You will get your quizzes back to review prior to your exam on Monday.  Many of you did very well, with only a few errors.
B-Day: If you are looking at this message you may as well take advantage of this quiz above, but your’s will now be substantially different, although the same principles will be assessed.

2-d-motion-study-guide-updated 2014
Updated from what’s in your packet.

 PreAP-notes-2D force inclined plane non-equilibrium
Notes from a prior class year, different examples and numbers, but same scenarios we looked at.

Be sure to review projectiles, including your last quiz and the items previously posted.


AP-C: Momentum problems and quiz key

APC momentum quiz KEY and extra problems


AP-1: 2D force analysis practice answer key

Worksheet–2D force analysis–KEY


AP-1: Marshmallow Catapult project info

Project–Marshmallow Catapult Project–PreAP–rev 2014

Project–Marshmallow Catapult Rubric–PreAP–rev. 2014

Project–marshmallow catapult data info

Formal lab outline, rev Fall 2014


AP-1 Projectiles notes and HW notes

Your class notes with problems completely worked out:

PreAP Projectile Notes-problems worked out

PreAP projectile examples

Also a few notes about your HW:

One reminder: These are all full-trajectory problems.  If, in the y-direction, you use the velocity at the top to be zero, recognize that the time you find with this data will be one-half of the total flight time.  You can use this time to find the max height, but you will need to double it to find the horizontal (x) distance traveled by the projectile.

Good luck!  Email me if you have questions.

That is a perfect example of a full trajectory problem.

1) You are given the initial velocity to start and it is a vector in both the x- and y-directions.  You must break it into x- and y-components, respectively Vx and Voy.  Put these numbers into your table of variables just like the example we looked at.
2) If you use the y-direction to solve for time as you must in this problem, you have the positive initial velocity (from #1 above), the negative acceleration of gravity and we know the velocity at the top of its trajectory is zero.  If you use this info to solve for time, recognize that you have found the time to go up, and that the total time that you will use in the x-direction is actually twice this much.

This is a horizontal projectile, but with weird information to start.  There is nothing special about it, it just begins with different information than what I used as an example in class.

This is the hardest problem on the assignment, in my opinion.  If you set up your table of x- and y-variables you will have two unknowns in both directions: Vo and t.  You can solve this just like a system of equations in math…2 equations, 2 unknowns, one from the x-direction and one from the y-direction.  The only tricky part is to do as described in number 1 above…make sure your Vx=Vocos(theta) and Voy=Vosin(theta).
This is sort of your challenge problem on this assignment.  I won’t do the rest for you, so give it a good shot.

This is a tougher problem in some ways than the others since the trajectory is interrupted by hitting the wall.  Unlike most of the other problems, you actually start with enough info to find the time it takes to hit the wall by using the x-direction (you know initial velocity, so find Vx and Voy, and use the horizontal distance to the wall).  This gets you the time for a and the time you need to use in part b.

Watch your units!  There are non-standard SI units in many questions.  Fix them before you begin.


AP-C: Conservation quiz KEY

Don’t forget to do the “take home quiz” as well.

AP-C–KEY–Conservation of energy quiz

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