A car having a total mass of 2250 kg and traveling at 72 km/h smashes into a tre

Question

A car having a total mass of 2250 kg and traveling at 72 km/h smashes into a tree. The car is stopped in 0.25 s. The driver of the car is not held in place by a seat belt or any other restraining device. Just after the impact but before the driver hits any part of the car, the acceleration of the driver is

PLEASE SHOW WORK

A) 80 m/s2 toward the tree.

B) zero with respect to the tree.

C) 80 m/s2 away from the tree.

D) 1.8 × 102m/s2 with respect to the car.

E) 37 m/s2 away from the tree.

I KNOW THE ANSWER IS B, BUT DON'T KNOW WHY.

Explanation / Answer

Q1.

With respect to tree, speed of car and diver before collision is 72 km/h.

When car just heat the tree, car starts decelerating due to retarding force due to tree. But there is no force on the driver until he touches any part of car(assuming there is no friction between sheet of car and driver body). So driver still moves with speed 72 km/h.

Hence acceleration of driver before he hits any part of car is 0 m/s^2 with respect to tree.

So, correct option is (B) Zero with respect to tree.      

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