Question

Superman must stop a 190-km/h train in 150 m

to keep it from hitting a stalled car on the tracks.
Part A
If the train's mass is 4.0-105 kg, how much force must he exert (find the magnitude)? Express your answer using two significant figures.
Part B
Compare to the weight of the train (give as %)
Part C
How much force (in magnitude) does the train exert on Superman

Answer 1

Part A:

Force = mass x acceleration

Acceleration = (final speed - initial speed) / time

final speed = 0, initial speed = 190 km/h, time = 150 m / 190 km/

Force = 4.0-105 x (0 - 190) / 1/324

Force ~ = 1.7 x 10^6 Newtons (N)

Part B:

Force from Superman / Weight of train =

1.7 x 10^6 / 4.0 x 10^5 = 425%

Part C: Force from train on Superman = Force from Superman on train

1.7 x 10^6 / 4.0 x 10^5 = 425%

Therefore, the train exerts 425% of the force that Superman exerts on the train, on Superman.