Poder: problemas e solucións

Power is the rate at which work is done in a given period. Mathematically, power is the work/time ratio.

P = W/t

Description: P = power (Joule/second = Watt), W = work (Joule), t = time interval (second)

Based on this equation, it can be concluded that the greater the work rate, the greater the power. On the other hand, the smaller the work rate, the smaller the power. Work rate refers to the rate at which work is done.

Power is a scalar. The SI unit of power is the Joule/second. The Joule/second = Watt (abbreviated as W), named so to pay homage to James Watt. The British imperial unit for power is foot-pound per second.

This unit is too small for practical purposes, so the greater unit horsepower (abbreviated as hp) is used. One horsepower = 550 foot-pound per second = 764 Watt = ¾ kilowatt.

The amount of work can also be expressed in power x time units, for instance, kilowatt-hour or kWh. One kWh refers to the work done at a constant rate of 1 kiloWatt for one hour.

1. Un peso de 50 kg person runs up the stairs 10 meters high in 2 minutos. Acceleration debido a gravity (g) is 10 m/s². Determine o poder.

Coñecido:

Masa (m) = 50 kg

altura (h) = 10 méteres

Aceleración debida á gravidade (g) = 10 m/s²

Intervalo de tempo (t) = 2 minuto = 2 (60) = 120 segundos

Querido : poder (P)

Solución:

Formula of power :

P = W / t

P= poder, W = traballar, t = tempo

Formula of Work :

W = F s = wh = mgh

W= traballar, F = facer, w = peso, d = desprazamento, h = altura, m = mass, g = aceleración debida á gravidade

W = mgh = (50)(10)(10) = 5000 Joules.

P = W / t = 5000 / 120 = 41.7 Joule/second.

2. Calculate the power required of a 60-kg person who climbs a tree 5 meters high in 10 seconds. Acceleration due to gravity is 10 m/s².

Coñecido:

Masa (m) = 60 kg

altura (h) = 5 meters

Aceleración debida á gravidade (g) = 10 m/s²

Intervalo de tempo (t) = 10 segundo

Querido : poder

Solución:

Traballo:

W = mgh = (60)(10)(5) = 3000 Joules

Poder:

P = W / t = 3000 / 10 = 300 Joule/second.

3. A rotary comedy with a power of 300 watts and period of 5 minutes rotates 5 rounds. The energy it uses is ….

15 kJ

75 kJ

C. 90 kJ

450 kJ

Coñecido:

Power (P) = 300 Watt = 300 Joule/second

Period (T) = 5 minutes = 5 (60 seconds) = 300 seconds

Number of rotation = 5

Quería: Energy used by the rotary comedy

Solución:

A resposta correcta é D.

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