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A car traveling east and a minivan traveling south collide in a completely inelastic collision at a perpendicular intersection.If the initial speed of the 1500kg car was 80.0km/h and the initial speed of the 3000kg minivan was 46.0km/h , what is the speed of the vehicles immediately after collision? What is the direction of the velocity of the vehicles immediately after collision?
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Added Fri, 26 Jun '15
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According to law of conservation of momentum, p before = p after.
Also, because this is an completely inelastic collision, the two vehicles will stick together afterwards.

Let's start talking about p before. We need to find the components of p: px and py because p = sq. root px^2 + py^2.

px=px1 + px2 where px1 is the x component of the car, and px2 is the x component of the van.
p=mv
px = m1vx1 + m2vx2 = (1500 kg)(80 km/hr) + (3000 kg)(0) = 120000 kg*km/hr
the x component of the van is 0 because it's travelling South.

py = m1vy1 + m2vy2 = (1500 kg)(0) + (3000 kg)(46 km/hr) = 138000 kg*km/hr

p before = sq. root px^2 + py^2 = sq. root 120000^2 + 138000^2 = 182877

p before = p after = 182877 kg*km/hr.

okay p= mv so v = p/m
m = 3000 kg + 1500 kg = 4500 kg.
v=(182877/4500)=40.6393 km/hr (1000m/ 1km) (1 hr/ 60 min) (1 min/60 s) = 11.2887 m/s

to find the angle, we do arc tan py/px: 49 degrees Southeast.
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Added Fri, 26 Jun '15
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