1. Which of the following statements is true about a system of two particles? Ex

Question

1. Which of the following statements is true about a system of two particles? Explain your answer.
a) it is possible for the system to have net zero momentum, but a net non-zero kinetic energy
b) it is possible for the system to have net zero kinetic energy, but a net non-zero momentum
c) Both a and b are possible
d) neither a nor b are possible


2. A car of mass m and speed v has a head-on collision with a truck of mass 2m and speed v/2. Which has the greater momentum change? Explain your answer.
a) the car
b) the truck
c) both have the same momentum change
d) it is impossible to say without knowing the velocities after the collision

Explanation / Answer

1 a) TRUE momentum depends on velocity directions sum of momentum of two particles can be zero but KE is not zero b) FALSE if KE is zero then velocity has to be zero so Momentum = 0 c) Both can not be possible as b is never possible d) neither a nor b are possible - FALSE because a is possible 2) mv +2m(-v/2) = final momentum 0 = m v1 + 2m v2 v1 = -2v2 change in momentum of car = m v1 - mv truck = 2m v2 - 2m(-v/2) = 2m(-v1/2) + mv = mv - mv1 SAME MAGNITUDE

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