Homework Help: physics

Posted by kdhgwiu on Tuesday, February 26, 2008 at 4:24pm.

need help on this three part one
its about inelastic collisions momentum and energy related with work

Find the speed at which Superman (mass=76.0 kg) must fly into a train (mass = 17620 kg) traveling at 60.0 km/hr to stop it.

Running into the train at that speed would severely damage both train and passengers. Calculate the minimum time Superman must take to stop the train, if the passengers experience an average horizontal force of 0.430 their own weight.

How far does the train then travel while being slowed to a stop?

physics - bobpursley, Tuesday, February 26, 2008 at 4:39pm
first, use conservation of momentum to find superman must fly.

Second, use impulse=change of momentum
You are given the average force.

averageforce*time=weight/g *velocity
.43avgweight*tim=avgweigh/g *velocity
solve for time

Lastly, the average velocity stopping is 30km/hr, you know the time, so solve for distance.
physics - derek, Sunday, April 4, 2010 at 10:55am
first part:
Pi=Pf
Pf=0 (train is not moving)
0= m1v1 + m2v2
v2=m1v1/m2

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