A pulley is used to lift a heavy mass from the floor to the platform. The IMA of the system is 5 and the AMA is 2.5. What is the
2 answers:
Answer:
efficiency= or 50%
Explanation:
IMA means Ideal Mechanical Advantage, and it indicates the ratio between the input forces and the output forces without taking into consideration the force needed to overcome friction. In pulleys, this is calculated by counting the number of ropes on the system that in this case is 5
IMA = 5
IMA is greater to the AMA because it doesn't take into consideration friction.
AMA is the Actual Mechanical Advantage, and it is the measure of the usefulness of the pulley, and it indicate the ratio between the output force (Fo) and the input force (Fi). The smaller this ratio, the less useful is the pulley, meaning, it does not simplify the job it is designed to ease, for example, a pulley that does not reduce the force needed to lift a load.
AMA=2.5
So from these two definitions, if we have the actual force ratio and the ideal force ratio, we basically have the "what it is" and the "what could be", a very crude representation of efficiency:
efficiency= or 50%
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First of all, we need to write the First Law of thermodynamics assigning the correct sign convention:
where
is the change in internal energy of the system
Q is the heat absorbed/released
W is the work done
and the signs are assigned based on whether there is an increase in the internal energy or not. Therefore:
Q is positive if it is absorbed by the system (because internal energy increases)
Q is negative if it is released by the system (because internal energy decreases)
W is negative if it is done by the system on the surrounding (because internal energy decreases)
W is positive if it is done by the surrounding on the system (because internal energy increases)
Using these definitions, we can now fill the text of the question:
When a system is heated, heat is ABSORBED by the system. The amount of heat added is given a POSITIVE sign. When a system is cooled, heat is RELEASED by the system. The amount of heat is given a NEGATIVE sign. If a gas expands, it must push the surrounding atmosphere away. Thus, work is done BY the system and is given a NEGATIVE sign. If a gas is compressed, then work is done ON the system. This work is given a POSITIVE sign.
Complete question:
A small 175-g ball on the end of a light string is revolving uniformly on a frictionless surface in a horizontal circle of diameter 1.0 m. The ball makes 2.0 revolutions every 1.0 s. What are the magnitude and direction of the acceleration of the ball?
Answer:
The acceleration of the ball is 78.98 m/s², directed inwards
Explanation:
Given;
mass of the ball, m = 175 g
radius of the circle, r = 0.5 m
angular speed of the ball, ω = 2 rev/s
The magnitude of the centripetal acceleration of the ball is calculated as follows;
The centripetal acceleration is directed inwards.