You are helping a friend move to a new apartment in another town. The two of you

Question

You are helping a friend move to a new apartment in another town. The two of you, the truck, and all her possessions weigh 3,600 kg. You are on a two-lane highway and have just slowed down to 15 mph (6.7 m/s) because you

You are helping a friend move to a new apartment in another town. The two of you, the truck, and all her possessions weigh 3,600 kg. You are on a two-lane highway and have just slowed down to 15 mph (6.7 m/s) because you're in a school zone. It's a good thing you did because a group of first graders are just starting to cross the road. Just after you pass the children, someone in a 900 kg sports car in the other lane is headed straight for the kids at 80 mph (35 m/s). You have an idea to cross over into the other lane to hit the sports car head-on. You want your truck and the sports car to crumple into a heap that sticks together and doesn't move, or at least moves away from the children. You are in both a moral and physical dilemma. Using physics concepts, mathematically show whether you save the children or if this is just a suicidal act? If not, how fast do you need to be going to just stop the sports car? How does the force of the truck on the car compare with the force of the car on the truck; is it greater, less, or the same? Which vehicle would you rather be in? What is the change in momentum delta p= pfinal-pinitial of the truck (write out the general equation in terms of masses and velocities)? What is the change in the momentum of the car? Which one is greater, or are they the same?

Explanation / Answer

1) conservation of momentum

3600*6.7 + 900*-35 = (3600+900)*v

v=-1.64 m/s

wont stop them

to stop

3600*v + 900*-35 = 0

v=8.75 m/s

2)forces are the same, rather be in truck

since will have smaller a

3) dp = 3600*-1.64-3600*6.7=-30000

dpcar = -900*1.62-900*35 =-30000

they are the same

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