How much force does the train exert on Superman?

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SUMMARY

Superman must exert a force to stop a train traveling at 120 km/h over a distance of 150 meters. The train has a mass of 3.6 x 105 kg, and the calculated deceleration is -3.703 m/s2. Using Newton's second law (F=ma), the force Superman needs to exert can be determined. According to Newton's third law, the force the train exerts on Superman is equal in magnitude and opposite in direction to the force he applies.

PREREQUISITES
  • Understanding of Newton's laws of motion, specifically Newton's second and third laws.
  • Basic knowledge of kinematics, including concepts of speed, distance, and time.
  • Ability to perform calculations involving mass, acceleration, and force.
  • Familiarity with unit conversions, particularly between km/h and m/s.
NEXT STEPS
  • Calculate the exact force Superman must exert using the formula F=ma with the given mass and deceleration.
  • Explore the implications of Newton's third law in real-world applications, particularly in collision scenarios.
  • Review kinematic equations to deepen understanding of motion and stopping distances.
  • Investigate the effects of different masses and speeds on the required stopping force in similar scenarios.
USEFUL FOR

Students studying physics, particularly those focusing on mechanics and forces, as well as educators seeking to explain practical applications of Newton's laws.

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Homework Statement



Superman must stop a 120-kmh train 150m to keep it from hitting a stalled car on the tracks. If the train's mass is 3.6 x 10^5 kg, how much force must he exert? Compare to the weight of the train (give as %). How much force does the train exert on Superman?"


Homework Equations



We just started this unit but I am not entirely sure which equation to use. I know I must find the amount of time it takes to stop, the deceleration of the train, and the forces from the problem.


The Attempt at a Solution



So far I've found the time, 9 seconds, and the deceleration, -3.703 (would it be negative?) I need help from this point on and I know it's relevant to Newton's third law of motion. Any help is greatly appreciated.
 
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Since you have the deceleration, use Newton's 2nd law and find the force. F=ma.
 
First of all, deceleration includes a negative sign. So it would be negative acceleration or positive deceleration.

The first step in your answer is to find the deceleration which you have done and it looks correct to me.

Newton's second law and Newton's third law overlap here. You know that force equals mass multiplied by acceleration. You have an acceleration and a mass so the force should be easy to find. As for Newton's third law. If Superman is applying 'x' amount of force, the train applies 'x' amount of force back.
 

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