HW-Sec 1-Prob 13 - F net = m • a F net represents the net...

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Robb Page 17-Feb-2010 Physics 140 Professor Stoddard Chapter 1 – Problem 13 Ques. How much force must a locomotive exert on a 12,000-kg boxcar to make it accelerate forward at 0.4 m/s 2 ? The boxcar will move in response to the net force applied to it, taking into consideration all the individual forces present. We have no information about frictional force, so for the moment we will assume it to be negligible. Since we know that the locomotive is the primary directional force, and that the acceleration depends on the strength of the net force and the mass of the object acted upon, we should be able to calculate the relationship. The acceleration, represented as a , is horizontal/forward at 0.4 m/s 2 . The mass of the boxcar is represented as the variable m in the equation below.
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Unformatted text preview: F net = m • a F net represents the net force . Therefore, the amount of force needed to move the boxcar is: F net = 12,000-kg • 0.4 m/s 2 = 4,800 N Pondering the 3 rd law: If we consider the oft cited phrase, “for every action, there is an equal and opposite reaction,” I tend to think that the size of the forces on both the locomotive and the boxcar as being equal. Which leads me down this path: “What propels the train forward is the directional force of the locomotive wheels applied to the track, for as the wheels spin the interaction with the track results in forces moving in opposite directions: train wheels forward, track backwards…essentially the force overcomes the mass of the boxcar, and it’s pulled along for the ride.”...
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