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Two masses 6.0 kg and 9.0 kg are hung from the two ends of a cord which passes over a smooth pulley
so that the two masses hang freely. If initially the 9.0 kg mass is 4 meters from the floor,
how long will it take this mass to reach the floor after the masses are released?
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The acting force in the system is the "net force", which is equal to the difference of the masses' weights
9*g - 6*g = 9*10 - 6*10 = 90 - 60 newtons = 30 newtons.
The total mass of the moving system is the SUM of the masses 6 kg + 9 kg = 15 kg.
THEREFORE, the acceleration of the masses is a = = 2 m/s^2,
according to the Newton's second law.
The time to reach the floor is determined by the equation for the uniformly accelerated body = 4 meters;
from this equation, t = = = = 2 seconds. ANSWER
Solved and carefully explained.