Consider a train moving at a constant velocity of 30 m/s. If the engines provide

Question

Consider a train moving at a constant velocity of 30 m/s. If the engines provide 4000 N of thrust, what is the frictional force acting on the train?

Consider a box placed on a rough plank of wood (i.e. consider friction). As the plank of wood is raised, what condition must be met for the box to start to slide?

Using Newton's First Law to answer, is your weight (i.e. force of gravity) the only force acting on you as you stand stationary on the floor?

Please answer in sentences and details. Thanks!

Explanation / Answer

constant velocity means a =0

Fnet = ma = 0

Fnet = Fthrust - friction = 0

friction = Fthrust = 4000 N





2.
then gravity component along plank > friction force

mgsin@ > u. mgcos@

tan@ > u

@ > tan-1(u)


u - friction coefficient




3 .

as we stand on ground we will be exerting some force on ground .

so from newtons 3rd law , surface will also exert a contact force on you in opposite direction.


so other than wight there is also contact force .

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