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CIE A Level Physics復習筆記5.1.5 Derivation of P = Fv

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年8月16日下午12:25

Derivation of P = Fv

Moving power is defined by the equation:

5.1.7-Moving-power-equation

This equation is only relevant where a?constant force?moves a body at?constant velocity. Power is required in order to produce an acceleration
The force must be applied in the?same?direction as the velocity

Derivation

The derivation for this equation is shown below:

5.1.7-Derivation-of-moving-power Derivation of P = F?× v

Worked Example

A lorry moves up a road that is inclined at 14.5° to the horizontal. WE-P-FV-question-image

The lorry has mass 3500 kg and is travelling at a constant speed of 9.4 m s-1. The force due to air resistance is negligible.Calculate the useful power from the engine to move the lorry up the road.

5.1.7-Worked-example-P-fv-2

Exam Tip

The force represented in exam questions will often be a drag force. Whilst this is in the opposite direction to its velocity, remember the force needed to calculate the power is equal to (or above) this drag force to overcome it therefore you equate it to that value.

轉載自savemyexams

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