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Jan
13

AP-1: Momentum HW #23

#26: This is your challenge problem and it is very hard, possibly beyond many of your abilities.  Do not fret!  It’s a bonus! Also, I cannot imagine a question this difficult, using the required knowledge base on your AP exam this spring.

#23:
This is a great question, and, I think, very much AP like in that it requires you to apply lots of different physics to solve the final part of the problem.

The diagrams in Figure 9-13 show a brick weighing 24.4 N being released from rest on a 1.00 m frictionless plane, inclined at an angle of 30.0°. The brick slides down the incline and strikes a second brick weighing 35.8 N.

There are actually three parts to this problem.  1) Sliding down the ramp.  2) The inelastic collision between the two objects.  3) Sliding with friction, coming to a stop.

Part 1)

You must apply your knowledge of ramps/inclines to find the speed of the object as it reaches the bottom of the ramp.  This “final velocity” will serve as object 1’s initial velocity during the collision.

Part 2)
You must perform a conservation of momentum calculation on the inelastic collision, using your solution from part 1 as your initial velocity.  You are looking for the final velocity of both (they move together, it’s the same) after the collision.  This final velocity will become the initial velocity in part 3 (see a pattern, yet?)

Part 3)
You need to assess with Newton’s 2nd Law.
{F = ma   only force is Ff and is back/negative
-Ff = ma   Mass is combined mass, a = (delta) v/t
You know the initial velocity is the final speed from part 2, and the final velocity here will be zero (it comes to a stop), Ff = mu*N, N=(m1+m2)*g
Solve for t
Use t to find x by kinematics

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