Question:
A machine which is 75% efficient, uses 12 J of energy in lifting 1 kg mass through a certain distance. The mass is then allowed to fall through the same distance. The velocity at the end of its fall is
A machine which is 75% efficient, uses 12 J of energy in lifting 1 kg mass through a certain distance. The mass is then allowed to fall through the same distance. The velocity at the end of its fall is
Updated On: Jun 20, 2022
- $ \sqrt{12} \, ms^{ - 1}$
- $ \sqrt{18} \, ms^{ - 1}$
- $ \sqrt{24} \, ms^{ - 1}$
- $ \sqrt{32} \, ms^{ - 1}$
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The Correct Option is B
Solution and Explanation
Potential energy of the mass at a height above the surface is given by
$ = \frac{ 75 }{ 100 } \times 12 = 9 $ J $ \hspace20mm$ ..(i)
Now, KE of the mass at the end of fall
KE = $ \frac{1}{2} mv^2 $ $ \hspace20mm$ ..(ii)
Applying law of conservation of energy
$ \frac{1}{2} mv^2 = 9 $
v = $ \sqrt{ \frac{ 2 \times 9 }{ m }} $
$ \sqrt{ \frac{ 18 }{ 1}} = \sqrt{18 } \, ms^{ - 1}$
$ = \frac{ 75 }{ 100 } \times 12 = 9 $ J $ \hspace20mm$ ..(i)
Now, KE of the mass at the end of fall
KE = $ \frac{1}{2} mv^2 $ $ \hspace20mm$ ..(ii)
Applying law of conservation of energy
$ \frac{1}{2} mv^2 = 9 $
v = $ \sqrt{ \frac{ 2 \times 9 }{ m }} $
$ \sqrt{ \frac{ 18 }{ 1}} = \sqrt{18 } \, ms^{ - 1}$
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Concepts Used:
Work, Energy and Power
Work:
- Work is correlated to force and the displacement over which it acts. When an object is replaced parallel to the force's line of action, it is thought to be doing work. It is a force-driven action that includes movement in the force's direction.
- The work done by the force is described to be the product of the elements of the force in the direction of the displacement and the magnitude of this displacement.
Energy:
- A body's energy is its potential to do tasks. Anything that has the capability to work is said to have energy. The unit of energy is the same as the unit of work, i.e., the Joule.
- There are two types of mechanical energy such as; Kinetic and potential energy.
Read More: Work and Energy
Power:
- Power is the rate at which energy is transferred, conveyed, or converted or the rate of doing work. Technologically, it is the amount of work done per unit of time. The SI unit of power is Watt (W) which is joules per second (J/s). Sometimes the power of motor vehicles and other machines is demonstrated in terms of Horsepower (hp), which is roughly equal to 745.7 watts.
- Power is a scalar quantity, which gives us a quantity or amount of energy consumed per unit of time but with no manifestation of direction.