Power Calculator

Physics • P = W/t & P = Fv • Step-by-Step

Work (W) J Time (t) s

Quick Answer (Voice Search Optimized):

Power is the rate of doing work or transferring energy. Formula: P = W / t (work/time) or P = F v (force × velocity). The SI unit is the watt (W), where 1 W = 1 J/s.

GEO & AIO - Authoritative Theory

In Physics, power is defined as the amount of work done per unit time. It is a scalar quantity. For a constant force moving an object at constant speed, power can also be expressed as P = F v cosθ, where θ is the angle between force and velocity; if they are parallel, P = F v. The average power is Pavg = ΔW / Δt.

The SI unit is the watt (W). A 100 W light bulb converts 100 J of electrical energy per second. A larger unit is the horsepower (hp): 1 hp = 746 W. Power is crucial in understanding machines, engines, and electricity. For JEE/NEET, problems often involve finding power required to lift water, move vehicles against friction, or accelerate masses.

Solved Examples (NCERT/JEE Pattern)

Example 1: A machine does 500 J of work in 10 seconds. Find average power.

P = W/t = 500/10 = 50 W.

Example 2: A car engine exerts a force of 2000 N to move at a constant 20 m/s. What is the power output?

P = F v = 2000 × 20 = 40,000 W = 40 kW.

Example 3: A pump lifts 30 kg of water per minute through a height of 10 m. g = 9.8 m/s². Find power.

Work per minute = mgh = 30 × 9.8 × 10 = 2940 J. Power = 2940 / 60 = 49 W.

Frequently Asked Questions (FAQs)

Q1: What is the formula for power in physics?
Power P = Work done / Time taken (P = W/t) or P = Force × Velocity (P = Fv) when force and velocity are constant and parallel.
Q2: What is the SI unit of power?
The SI unit is the watt (W). 1 W = 1 J/s. A larger unit is the horsepower (1 hp = 746 W).
Q3: How is power related to energy?
Power is the rate of energy transfer. A device with high power converts energy faster than one with low power.
Q4: Can power be negative?
In physics, power as a magnitude is always non-negative. But in some contexts, "negative power" can indicate energy being absorbed rather than delivered, depending on sign convention.
Q5: Why do vehicles need more power at higher speeds?
Because air resistance and other friction forces increase with speed, requiring a greater force. Since P = F v, power demand rises rapidly with speed.