physics
posted by Elisa .
A 3.6 kg mass hangs at one end of a rope that is attached to a support on a railroad car. When the car accelerates to the right, the rope makes an angle of 1.0° with the vertical. Find the acceleration of the car.

The vertical component of the rope tension equals the weight (M g) and the horizontal component equals the acceleration (M a). The ratio of horizontal to vertical components is the tangent of the tilt angle with respect to vertical.
Use those facts to solve for the acceleration, a 
"M a" is the accelerating force, not the acceleration itself.
The rest of my previous answer is correct.
tan 1.0° = 0.01746 = Ma/Mg = a/g
Solve for a. g = 9.81 m/s^2
The 3.6 kg mass M does not matter. It cancels out.