1.22 Plenary questions

Physics for You p.147

 

a)      Momentum = mv

Momentum = (2+6) x 8

Momentum = 64 kgm/s

b)      See exercise book

c)      KE is not conserved it is converted and wasted as other forms of energy.

 

1.22

 

1.22

Tuesday, July 06, 2010

3:04 PM

·        1.22 use the conservation of momentum to calculate the mass, velocity or momentum of objects

Momentum conserved in collisions

	<<AirTrack simulation.swf>>
			and 1.20 animation

Momentum conserved in explosions

			<<newtons_cradle[1].swf>>
	<<N3L - Every action has a Gun fire.mpeg>>

Example - Pearson, p.41

 

Consider final momentum

 

Truck, plasticine and pellet

p = m x v

p = (0.1+0.002) x 0.8

p = 0.0816kgm/s

 

total final momentum = p_f = 0.0816kgm/s   

 

Principle of Conservation of Momentum tells us:

total initial momentum = total final momentum

                               Σp_i = Σp_f

 

so total initial momentum = p_i = 0.0816kgm/s

 

 

Consider initial momentum

 

Truck and plasticine   

p = m x v

p = 0.1 x 0

p = 0kgm/s 

 

Pellet   

p = m x v

0.0816 = 0.002 x v

v = 40.8m/s

 

 

1.22 animation

14 March 2012

15:49

 

Website:

http://www.walter-fendt.de/ph14e/collision.htm

 

Embed code for your blog:

 

Example:

http://maddog11physics.posterous.com/conservation-of-momentum-animation#

newtons_cradle[1].swf Download this file

AirTrack simulation.swf Download this file

Investigating Momentum

Starter - Spot the mistakes!

13 March 2012

16:35

·        http://sites.google.com/site/winfailphysics/all-videos/roadrunner-human-cannonball

·        http://sites.google.com/site/winfailphysics/all-videos/roadrunner-spring-punch

·        You know that these situations are wrong, but why are they wrong?!

 

 

 

Guided discovery - Investigating Momentum

14 March 2012

07:20

When we collide two gliders on the

air track, what happens?

 

Situation 1: Elastic collision with a stationary glider

Initial

Initial speed of LH glider = u_l = 1m/s

Initial speed of RH glider = u_r = 0m/s

 

Final

Final speed of LH glider = v_l = 0m/s

Final speed of RH glider = v_r = 1m/s

 

We can represent this graphically as

 

Initial

Final

 

Conclusion

·        It appears that the speed is "transferred" to the RH glider

 

 

Situation 2: Inelastic collision with a stationary glider

Initial

Initial speed of LH glider = u_l = 1m/s

Initial speed of RH glider = u_r = 0m/s

 

Final

Final speed of LH glider = v_l = 0.5m/s

Final speed of RH glider = v_r = 0.5m/s

 

We can represent this graphically as

 

Initial

Final

 

Conclusion

·        Speed is conserved in the collision

·        Total Initial speed = Total Final speed

 

 

Situation 3: Head on collision

Initial

Initial speed of LH glider = u_l = 1m/s

Initial speed of RH glider = u_r = -1m/s

 

Final

Final speed of LH glider = v_l = 0m/s

Final speed of RH glider = v_r = 0m/s

 

We can represent this graphically as

 

Initial

Final

 

Conclusion

·        Velocity is conserved in the collision

·        Total Initial velocity = Total Final velocity

 

 

Situation 4: Head on collision with different masses

Initial

Initial speed of LH glider = u_l = 1m/s

Initial speed of RH glider = u_r = -1m/s

 

Final

Final speed of LH glider = v_l = 0m/s

Final speed of RH glider = v_r = 0m/s

 

Problem!

Our previous conclusion that

o   Velocity is conserved in the collision

doesn't hold for this situation!

 

Why do they move off to the left?

Because the RH glider has twice the mass

 

What could I change about the LH glider to make both gliders stop after the collision?

o   Double the mass (obvious)

o   Double the initial velocity

 

We can represent this graphically as

 

Initial

Final

 

So something is conserved in the collision, but what is it?

 

What does the area of the rectangles represent?!

 

Time to label our axes!

Final Conclusion

·        The area of the rectangles are mass x velocity

·        Momentum = mass x velocity

·        So momentum is conserved in collisions

1.20

 

1.20

Tuesday, July 06, 2010

3:04 PM

·        1.20 recall and use the relationship between momentum, mass and velocity:         

           momentum = mass × velocity                   

                             p = m × v

p = m × v

p = momentum (kgm/s)

m = mass (kg)

v = velocity (m/s)

Homework for Monday 12.03.12

a.    How ²³⁵U is made unstable

235U is made unstable by the adding of a neutron the the parent nuclei.

b.    How a chain reaction can occur

A chain reaction occurs when Uranium 235 atom splits, three neutrons are emitted and these may hit three other uranium atoms so that they split and emit more neutrons which in turn hit other atoms and so on.

c.    How a chain reaction can be controlled

Chain reactions can be controlled by movable control rods, made out of boron or cadminum. They absorb neutrons in order to reduce or stop completley the chain reaction.