A train is moving at a constant speed on horizontal rails. Then from Newton’s laws it can be inferred that-

(a) the engine is shut off

(b) the engine is necessarily providing a constant driving force

(c) the engine supplies a constant power

(d) no force acts on the train

here we have two cases

1) if there is no friction bw rails & tyre & train is moving with constant velocity then ,

there will be no force acting on the train along horizontal direction & option a) is correct...

2)but if there exists friction & train is moving with constant velocity then ,

there exists a constant force which is along the direction of motion and equal in magnitude of friction force...

we know power = F*V = product of force & velocity

when both force & velocity are constant then power will also become constant so for this case

b) , c) are correct

the answer is d

as

if there is friction then a is wrong

if there is no friction then b and c are wrong

dear shivam,

in ideal conditions, that is, if there is no friction between rails and wheels then answer (A) the engine is shut off must be correct,

but in practical conditions , there exists a friction, therefore answer must be (B).

since nothing is mentioned about the friction we will assume practical conditions hence answer must be (B)

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AMAN BANSAL

option d is correct, no force is acting on the train as the force due to friction is cancelled by the driving force