10/30 Momentum in 2D

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10/30 Momentum in 2D

• Text Chapter7
• HW 10/28 HW Handout 2-D Momentum Due
  Thursday, 10/31
• HW 10/30 HW Handout 2-D Momentum and Energy
  Due Friday, 11/1
• Exam 3 Thursday, 11/14
• Exam 4 Thursday, 12/5
• Final Exam Monday, 12/16, 800 am

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10/28 HW part a)
p1,f p2,f psys,i since no net force on the
system
Components of p1,f are 20kg m/s for both up and
left.
So the components of p2,f must be 20kg m/s for
both down and left.
p2,f is then 28kg m/s at 45 below horizontal.
v2,f is then 14m/s at 45 below horizontal.
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Methods for Momentum

• psys,i psys,f
• Best when things stick together
• ?pA ?pB
• Good when you know velocity before and after for
  one object
• Components for 2-D
• Can find components first

4
A car and a truck, velocities and masses shown,
collide and lock bumpers. Find the final
velocity (magnitude and direction) of the pair.
y
vf
vc 15 m/s
?
370
Mc 2000 kg
x
pt,i,y ?
24,000 kg m/s
pc,i,y ?
0
vt 5 m/s
psys,f,y ?
24,000 kg m/s
pt,i,x ?
32,000 kg m/s
pc,i,x ?
30,000 kg m/s
Mt 8000 kg
psys,f,x ?
62,000 kg m/s
5
A car and a truck, velocities and masses shown,
collide and lock bumpers. Find the final
velocity (magnitude and direction) of the pair.
y
vf
vc 15 m/s
?
370
Mc 2000 kg
x
psys,f,y 24,000 kg m/s
psys,f,x 62,000 kg m/s
vt 5 m/s
psys,f ?
66,500 kg m/s
vsys,f ?
6.65 m/s
Mt 8000 kg
? ?
tan-1 24,000/62,000 21