# Find d with m and v

krisrai
If a 50 000 kg locomotive is traveling at 10m/s and its brakes and engine both fail, how far will it roll before coming to a stop.

Now I know how to do this problem if friction was given but I really don't know which formulas i can combine.

I think I need to find deceleration but I don't know how with the information given.

If someone could give me a hint how to get started it would be appreciated:)

Homework Helper
Are you sure that is all the question gave? Because if you ignore friction, then there must be some other force acting on the train, else by Newton's first law, that train should continue to move in a straight line.

warmfire540
sorry man, there is no way to find this..because we need to find the deceleration..which is either
a. negative acceleration because of engine
b. negative acceleration because of friction

we know that it's v=10ms-1, but we don't know a time or accel

krisrai
i know, if there was friction i could use ma=mgUs and find acceleration to sub into a kinematics formula to find d skidding

the question oly gives what i wrote above

krisrai
my textbook gives the answer as 2550m

SheldonG
If a 50 000 kg locomotive is traveling at 10m/s and its brakes and engine both fail, how far will it roll before coming to a stop.

Now I know how to do this problem if friction was given but I really don't know which formulas i can combine.

I think I need to find deceleration but I don't know how with the information given.

If someone could give me a hint how to get started it would be appreciated:)

I think you can assume the engine is running constantly, providing a force to push the train. But the train is not accelerating, it is traveling at 10 m/s. When the engine fails, the resistive force that keeps the train traveling at 10 m/s is the only force remaining, since the brakes also fail.

Sheldon

krisrai
definitely helps thank you hage
I just wasnt expecting that i would have to look up the coefficient of rolling friction like pingpong did.

Homework Helper
Yeah, I agree that's a bit strange.