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# 10pts to whomever can help me with this physics prob the best!?

Superman must stop a 150 km/h train in 190 m to keep it from hitting a stalled car on the tracks.

a) If the train's mass is 4.0×105 kg, how much force must he exert (find the magnitude)?

b) Compare to the weight of the train (give as %).

c) How much force(in magnitude) does the train exert on Superman?

10pts to the most detailed and CLEAREST answer. If you explain you steps with words as well, it would be a big bonus  1st step convert DATA to BASIC SI units:

V = 150 km/h = (150)(1000)/3600) m/s = 41.7 m/s

d = 190 m

a) m = 4.0e5 kg

KE of train = 1/2mV² = (0.5)(4.0e5)(41.7)² = 1739(2.0e5) = 3.48e8 J

Work to stop train in distance = d:

Favg x d = 3.48e8

Favg = 3.48e8/1.90e2 = 1.83e6 N ANS a)

b) Wt of train = 4.0e5 x 9.81 = 39.24e5

Favg/Wt =1.83e6/3.92e6 = 0.467 ANS b)

c) force of train on S-man = Favg = 1.83e6 N ANS c)