2016+Momentum

=Unit 4: Momentum=

Friday



Monday



__ANSWERS__

page 209

1) 2842 kgm/s 2a) 121.05 kgm/s 2b) 94.5 kgm/s 2c) 26.55 kgm/s 3) 46.49 m/s

page 211

1) -375 N 2) We need to find the velocity that he hits the water with first, because that will be his momentum when he hits the water. So, using our motion equations we know that an object falling from a distance of 3 meters will be 7.67 m/s. So, momentum is 629 kgm/s. That drops to zero so the impulse is -629 kgm/s. So, divide that by time to get the force, which is -1144 N. It has to be negative because it's a stopping force. 3) Impulse = Pf - Pi. So, impulse = -16 kgm/s. (the final velocity was -22 m/s and the initial was 18 m/s) 4a) 9 m/s (Ft = change in momentum and the initial momenturm was zero) 4b) initial momentum = 4.5 kgm/s. The impulse provided by the force is 12 kgm/s in the opposite direction. So, the final momentum is -7.5 kgm/s. So, the final velocity is -15 m/s.

page 213

1) 13.75 m/s 2) 42.2 m 3) 8 seconds

page 214

1) doubled 2) 31.0 m/s 3) Not if the large force is given over a much smaller time comparitively. But, all things equal, a large force WOULD cause a greater change in momenturm because the change is equal to Ft 4) Momentum is a measure of the object's "mass in motion", or how much force it would take to stop the object. Impulse is the change in momentum due to some force either acting with the motion or opposing it. 5a) 2.52 kgm/s 5b) 126 N

Tuesday

[|Conservation of momentum worksheets]

1) 1 m/s 2) 1 m/s 3) 50 kg ("perfectly elastic means that ALL of the first object's momentum transfers to the 2nd object) 4) 4 m/s 5) 4 km/hr 6) 0.86 m/s 7) -1 m/s 8) 0.8 m/s 9) 2 m/s 10) v1 = -v2 (if everything else is equal, the final velocities have to be equal and opposite) 11) 1.25 m/s 12) 2 m/s east 13) -0.75 m/s 14) 2 m/s 15) 3 m/s

+3 TEST EXTRA CREDIT: Due on paper (fully worked out) by Thursday 3:05pm



Wednesday





__**PRACTICE TEST (Conceptual Questions)**__
1) What are the units of momentum and impulse? 2) How is impulse related to momentum? 3) If you provide an impulse to an object, in what circumstance will it slow down? In what circumstance will it speed up? In what circumstance will it turn? (think about it) 4) Explain in your own words the Law of Conservation of Momentum 5) Two children are standing still on ice and push off each other. Each has a momentum after the push. Doesn't this violate the conservation law? It was zero before the push. 6) Describe how the conservation law works with elastic and inelastic collisions. 7) When objects collide inelastically in 2-D, why can't you simply make a triangle with total Vx and Vys in order to find out the final velocity of the new object? Why doesn't that work? 8) In general, for elastic collisions with stationary objects, when will the first object bounce back? In general, when will it follow the stationary object after the collision?

__**PROBLEMS**__

1) A 5 kg car moving at 20 m/s collides with a 10 kg car traveling in the same direction at 3 m/s. Calculate the resulting velocities for BOTH cars for both elastic and inelastic scenarios. 2)

3)

4

1) You won't be able get a final answer for part a but you can get the equation with two unknown velocities. (thanks Alex)