Posted by alexa on Tuesday, July 12, 2011 at 1:31am.
A locomotive pulls a series of wagons. Which is the correct analysis of the situation?
A. because action always equals the reaction,the locomotive cannot pull the wagons,the wagons pull backward just as hard as the locomotive pulls forward, so there is no motion.
B. The train moves forward because the locomotive pulls forward slightly harder on the wagons than the wagons pull backward on the locomotive
C. the locomotive gets the wagons to move by giving them a tug during which the force on the wagons is momentarily greater than the force exerted by the wagons on the locomotive
D. the locomotive can pull the wagons forward only if it weighs more than the wagons
E. The locomotive's force on the wagons is as strong as the force of the wagons on the locomotive,but the frictional force on the locomotive is forward and large while the backward fricitonal force on the wagons is small.

physics  bobpursley, Tuesday, July 12, 2011 at 9:13am
Very poor question.
a. would be true if the word "accelerating" were inserted between "no motion". As it is, it is false
b. if Locomotive pulls means net force of the locomotive, it is false, unless the train is accelerating.
c. Again, true during the moment of acceleration.
d. nonsense
e. nonsense.
So the question is what does the question mean "a locomotive pulls a series of wagons" This is very indefinite. The central question is the train accelerating, constant motion (including stopped)?
I suspect Your instructor mean c to be the only right answer, but instructors get paid to do better than this.
If net force is greater than retarding force, acceleration happens. If net force is equal to retarding force, acceleration is zero, and the system remains in whatever motion it was in.
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