Tuesday
May 21, 2013

# Homework Help: physic

Posted by noah on Saturday, July 2, 2011 at 1:10am.

Superman must stop a 120km/h train in 150m to keep it from hitting a stalled car on the tracks.If the train's mass is 3.6x10^5kg,how much force must he exert?Compare to the weight of the train (give as%).How much force does the train exerts on Superman?

• physic - Henry, Saturday, July 2, 2011 at 7:43pm

Vo=120,000m/h * (1/3600)h/s = 33.33m/s.

a = (Vf^2 - Vo^2) / 2d,
a = (0 - (33.33)^2) / 300,
a = - 3.7m/s.

F = ma = 3.6*10^5 * (-3.7) = -13.3*10^5 = -1.3*10^6N = Force applied
in opposite direction of train's force.

• physic - noah, Sunday, July 3, 2011 at 12:52am

thx

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