Power Formula (P = W/t): Free Calculator & Worked Examples

How to calculate power with P = W/t (and P = Fv). Watts vs joules, unit traps, worked examples, and a free power calculator.

How to Calculate Power (Quick Answer)

Mechanical power is P = W/t (often written p = w/t). Divide work in joules by time in seconds. The answer is in watts (W), because 1 W = 1 J/s.

  • Write P = W ÷ t.
  • Convert work to joules and time to seconds (minutes × 60).
  • Divide. Check: same work in less time → higher power.
  • Rearrange: W = P × t, or t = W / P.

    • Need a checked number now? Open the free power calculator (P = W/t) — then come back for P = Fv, unit traps, and work vs power.

    What Is the P = W/t Formula?

    Power is how fast work is done or energy is transferred. Two jobs can transfer the same joules, but the one finished sooner has higher power. That is why homework writes p = w/t physics as work rate in watts.

    Work W is energy transferred (joules). Power P is the rate (watts). Do not mix the symbols: capital W for work and for the watt unit look the same in text — keep units clear (J vs W).

    The Formulas

  • P = W/t — power from work and time.
  • W = P × t — rearrange for work.
  • t = W / P — rearrange for time.
  • P = Fv — constant force F along motion at speed v.

    • P = Fv comes from P = W/t with W = Fd and v = d/t, so W/t = F(d/t) = Fv. Use it when the problem gives force and speed instead of total work.

    Solve P, W, or t on the free power calculator.

    Power vs Work

    Work is energy transferred — see how to calculate work (W = Fd) and the

    work calculator.

    Example: lifting 100 J in 2 s gives P = 50 W. The same 100 J in 10 s gives P = 10 W. Same work, different power.

    Exam traps on joules vs watts: Work vs Power Exam Traps.

    Units

  • Work W → joules (J). Convert kJ × 1000.
  • Time t → seconds (s). Convert minutes × 60.
  • Power P → watts (W). 1 W = 1 J/s.

    • Horsepower is a non-SI power unit — use the horsepower calculator when the question asks for hp.

    Circuit power is different: electric power (P = VI).

    Worked Examples

    Example 1: p = w/t for 600 J in 12 s

    P = W/t = 600 / 12 = 50 W.

    Example 2: find work from power

    P = 120 W for 25 s. W = P × t = (120)(25) = 3000 J = 3.0 kJ.

    Example 3: P = Fv

    F = 200 N at steady v = 3.0 m/s along the force. P = Fv = 600 W.

    Example 4: time for 1500 J at 75 W

    t = W/P = 1500 / 75 = 20 s.

    Check Examples 1–4 on the power calculator.

    Common Mistakes

  • Confusing power (watts) with work (joules) or weight (newtons).
  • Leaving time in minutes while work is in joules.
  • Using P = Fv when force is not parallel to velocity.
  • Mixing mechanical P = W/t with electric P = VI.

    • Free Power Calculator

    Use the free power calculator to solve P = W/t for power, work, or time with step-by-step working.

    Work calculator.

    Kinetic energy calculator.

    Electric power calculator.

    Master P = W/t with seconds and joules — then verify every homework answer.

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