Two students, Justin and Taylor, are discussing Newtons third law, which says th
ID: 1423192 • Letter: T
Question
Two students, Justin and Taylor, are discussing Newtons third law, which says that when objects interact with each other they satisfy the following principle:
If object A exerts a force on object B, then object B exerts a force back on object A and the two forces are equal and opposite.
They are asked to consider four situations concerning two identical cars and a much heavier truck.
1)The two cars hit each other coming from opposite directions at equal speeds.
2)One car is parked and the other car crashes into it.
3)One car is parked and the truck crashes into it.
4)The truck is pushing the car because the car’s engine cannot start. They are speeding up.
Justin says, "It will only hold in the first case." Taylor says, "No, I think some of the other cases might also work." What do you think? Explain whether you agree with Justin or Taylor and justify why you agree.
Explanation / Answer
in all the four situations, newton's third law is applicable.
case 1:
The two cars hit each other coming from opposite directions at equal speeds:
car 1 will exert a force on car 2 in the direction of car 1's motion i.e. opposite to the direction of car 2's motion and vice versa.
so that due to the opposite forces, each of the cars will slow down immediately and the resultant change in kinetic energy will be turned to thermal energy that creates damage in the case of a crash.
case 2:
One car is parked and the other car crashes into it.
car 1 is stationary and car 2 crashed into it from behind.
then car 2 will exert a force along its direction of motion on car 1 so that it will impart an impulse on car 1 that will result in change of momentum and car 1 will start moving. because of friction, and the conversion of initial kinetic energy into thermal energy, it will ofcourse stop after moving some distance
similarly, car 1 will exert a force on car 2 in ooposite direction to motion of car 2 that will make the car 2 slow down.
hence newton's third law applies.
case 3:
One car is parked and the truck crashes into it
same scenario as case 2 but the force exerted on stationary car will be higher due to higher momentum and kinetic energy of massive truck.
case 4:
The truck is pushing the car because the car’s engine cannot start. They are speeding up.
car pushes the truck back with same force as the truck in pushing the car with,
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