An unknown mass and a 1.00 kg mass are fixed at opposite ends of a bar. The bar has negligible mass and a length of 30.0 cm.
The bar balances when supported by a pivot placed 20.0 cm from the unknown mass, as shown. bar pivot 20.0 cm 1.00 kg mass 30.0 cm unknown mass
What is the unknown mass?
A 333 g
B 500 g
C 667 g
D 1000 g
ANSWER: B
The Physics behind the answer:
- The second condition of equilibrium is that the sum of clockwise moments equals the sum of counter-clockwise moments.
- The above leads to the equation (1.00 kg)(g)(10.0 cm) = (unknown mass)(g)(20.0 cm).
- After doing the mathematics, the unknown mass is determined i.e. 0.500 kg. This is option B.
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