Calculating Forces on Boxcars in a Train: Newtons and Acceleration

[waldvocm]

A train consists of a 4300kg locomotive pulling two loaded boxcars. The first boxcar has a mass of 12,700kg and the second 16,300kg. Presume that the boxcar wheels roll without friction and ignore aerodynamics. The acceleration of the train is 0.578m/s^2
a)With what force, in Newtons, do the boxcars pull on each other?

I am confused here. Do they pull on each other with the same force? They can't since they don't weigh the same, correct?

0.578=T/12700 T=7340.6

0.578=T/16300 T=9421.4


b) With what force do the locomotive and first boxcar pull on each other?

I can use the same steps from a) for this one

c)With what force must the tracks push on the locomotive?

would the force be equal to the weight?

 

[Doc Al]

Do they pull on each other with the same force? They can't since they don't weigh the same, correct?

What does Newton's 3rd law tell you?

0.578=T/12700 T=7340.6

0.578=T/16300 T=9421.4

Don't confuse the net force on a car with the force between the cars.

First things first. Draw diagrams of each car, showing the forces acting on it. Then apply Newton's laws as needed.

 

[waldvocm]

a) boxcars pull on each other
F=16300(0.578)=9421.4

b)The locomotive pull on the first boxcar
F=12700+16300(0.578)=16762

c)The tracks push on the locomotive
F=4300(9.80)=42140

Are these formulas correct?

 

[Doc Al]

a) boxcars pull on each other
F=16300(0.578)=9421.4

b)The locomotive pull on the first boxcar
F=12700+16300(0.578)=16762

c)The tracks push on the locomotive
F=4300(9.80)=42140

Are these formulas correct?

The first answer is correct, but the others are not. I suggest that you label the forces--for example, F_1-2, F_L-1, and F_t-L--then write force equations for each car.