A machine does 1000 J of work in 20 s. Power is MCQ with Answer and Explanation

A machine does 1000 J of work in 20 s. Power is
A. 20000 W
B. 5 W
C. 20 W
D. 50 W
Answer: Option D
Solution (By JKSSB Mock Tests)
P = 1000/20 = 50 W.

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Practice More Physics Questions

Question #1
A body of mass 2 kg has momentum 10 kg·m/s. Its kinetic energy is:
A. 12.5 J
B. 25 J
C. 100 J
D. 50 J

Correct Answer: Option A


Explanation:
KE = p²/(2m) = (10)²/(2×2) = 100/4 = 25 J. Wait, recalculate: 100/4 = 25 J. Option B is correct. KE = p²/2m relates momentum and kinetic energy. Memory tip: When given momentum, use KE = p²/2m instead of finding velocity first. Efficient calculation method for competitive exam time constraints.

This question belongs to: Science Physics
Question #2
Which thermodynamic process occurs at a constant volume?
A. Adiabatic process
B. Isobaric process
C. Isothermal process
D. Isochoric process

Correct Answer: Option D


Explanation:
An isochoric process is a thermodynamic process in which the volume of the closed system remains constant (delta V = 0). Because there is no change in volume, the system does zero pressure-volume work (W = Pdelta V = 0). According to the first law of thermodynamics, any heat added goes entirely into increasing the internal energy. Isobaric is constant pressure; isothermal is constant temperature.

This question belongs to: Science Physics
Question #3
Assertion: Pressure is scalar. Reason: Pressure acts equally in all directions at a point.
A. Both true, R explains A
B. A false, R true
C. Both true, R doesn't explain A
D. A true, R false

Correct Answer: Option A


Explanation:
Pressure is scalar (no direction), though force is vector. Reason: Pascal's law - fluid pressure transmits equally in all directions, confirming scalar nature. Memory aid: 'Pressure = force/area (scalar division); isotropic in fluids'. Assertion-reason testing fluid mechanics fundamentals, common in competitive exams.

This question belongs to: Science Physics