The figure shows a 100 kg block being released from rest from a height of 1.0 m. It then takes 0.90 s to reach the floor. What is the mass of the block on the left?
Illustration shows a pulley connected to the ceiling, with a block of 100 kg on the right, and a block of unknown mass on the left.
The Attempt at a Solution
I used this to find acceleration of the system:
0 = 1 + (0.5)(a) [(0.90)^2]
a = (-2.5) m/s^2
I drew a diagram. F_G on the bottom, 100 * 9.8 = 980N down.
F = ma so (100)(2.5) = 250, and that must mean that the vector pointing up in my diagram will be 730N (980 - 250 = 750).
So, the 750 comes from the other block. F = ma again, solve for m I get 292 kg, which is not the right answer.
Where did I go wrong?