A compact car, mass 650 kg, is moving at 100 km/hr toward the south. How do you find the magnitude and direction of its momentum? A second car, with a mass of 2175 kg, has the opposite momentum. What is its velocity?

1 Answer
A08
Feb 6, 2017

Let East direction be #+x#-axis and North direction be #+y#-axis.
Velocity of compact car of mass #m=-100haty" kmh"^-1#

Converting in SI units we get
Velocity of compact car#=-100xx1000/3600haty" ms"^-1#
#=.-1000/36haty" ms"^-1#

Momentum #vecp=mvecv#
Inserting values we get
Momentum #vecp=650xx(-1000/36)haty#
#=-1.80bar5xx10^4haty" kgms"^-1#
#:.# Magnitude of momentum #|vecp|=1.80bar5xx10^4" kgms"^-1#
Direction of momentum is #-haty# or south direction.

Second car has opposite momentum#=1.80bar5xx10^4haty" kgms"^-1#
Its velocity is#=1/m vecp#
#=1/2175 (1.80bar5xx10^4haty)#
#=>8.3haty" ms"^-1#, rounded to one decimal place.

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