 #1
mingyz0403
 12
 1
 Homework Statement:

Block B starts from rest, block A moves with a constant acceleration, and slider block C moves to the right with a constant acceleration of 75 mm/s2. Knowing that at t = 2 s the velocities of B and C are 480 mm/s downward and 280 mm/s to the right, respectively, use kinematics to determine:
a. The acceleration of A and B
b. The initial velocities of A and C
c. The change in positions of slider C after 3 s.
 Relevant Equations:

Motion equation.
Conservation of string
How do you set the direction for this problem? Do you look at the motion of the block? If you set right positive, does that automatically makes upward motion positive? I set right as positive and up as positive for this problem. However, my answer was wrong. Textbook solution set right as positive and down as positive. I don't understand why setting right as positive and up as positive wrong for this problem.
Many thanks for your help.
Many thanks for your help.