Question

A toy freight train consists of an engine and three identical cars. The train is moving to the right at constant speed along a straight, level track. Three spring scales are used to connect the cars as follows: spring scale A is located between the engine and the first car; scale B is between the first and second cars; scale C is between the second and third cars.

(a) If air resistance and friction are negligible, what are the relative readings on the three spring scales A, B, and C?
A ---Select---=<> B ---Select---=<> C

(b) Repeat part (a), taking air resistance and friction into consideration this time. [Hint: Draw an FBD for the car in the middle.]
A ---Select---=<> B ---Select---=<> C

(c) If air resistance and friction together cause a force of magnitude 6.0 N on each car, directed toward the left, find the readings of scales A, B,and C.

A	N
B	N
C	N

Answer 1

Answer questionfor part (a) there is no acceleration, so F = ma says no force on the spring scales A, B, or C.

For part (b) the first spring needs to pull three cars, so A has the biggest reading, the middle spring pulls two, so B has the middle reading, and C has to pull only one car, so it has the smallest reading.

For part (c) we add numbers. Now A has a reading of 6N + 6N + 6N = 18N

B is pulling two cars, so 12N

C is pulling the last car, so 6N

Answer 2