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Select the correct alternative(s).

A

Work done by static friction is always zero

B

work done by kinetic friction can be positive also

C

kinetic energy of a system can not be increased without applying any external force on the system

D

work energy theorem is not valid in non-internal frame

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question regarding the correct alternatives related to work, energy, and power, we need to analyze each option provided in the video transcript. ### Step-by-Step Solution: 1. **Option A: The work done by static friction is always zero.** - Static friction acts to prevent relative motion between two surfaces. If there is no relative motion, the displacement of the object due to static friction is zero, leading to zero work done. However, if the surfaces are moving together without slipping, static friction can do positive work. Therefore, this statement is **false**. 2. **Option B: The work done by kinetic friction can be positive also.** - Kinetic friction opposes the motion between two surfaces in contact. However, if we consider a scenario where both objects are moving in the same direction and kinetic friction acts on one of them in that direction, the work done by kinetic friction can indeed be positive. Therefore, this statement is **true**. 3. **Option C: The kinetic energy of a system cannot be increased without applying any external force.** - Kinetic energy can be increased by internal forces, such as during an explosion or deformation of materials. Internal forces can do work on the system, leading to an increase in kinetic energy without external forces being applied. Therefore, this statement is **false**. 4. **Option D: The work-energy theorem is not valid in non-inertial frames.** - The work-energy theorem can be applied in non-inertial frames by accounting for pseudo forces. By including the work done by pseudo forces, the theorem remains valid. Therefore, this statement is **false**. ### Conclusion: The correct alternatives from the options provided are: - **B** (The work done by kinetic friction can be positive also).
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