# Force of friction Question

An electric scooter is travelling at a speed of 30ms⁻¹ and is kept going against a 50 N frictional force by a driving force of 300 N in the direction of motion. Given that the engine runs at 200 V, calculate the current in the scooter.

Hi everyone,

the worked solution is P = Fv =300 * 30 = 9000
I = P/V = 9000/200 = 45 A

My question is why don’t we consider the frictional force in the calculation?
Why is the first equation not P = Fv = (300-50) * 30???

Thanks!

the rate at which work is done on the scooter, and it is equal to the driving force multiplied by the speed of the scooter. In this case, the driving force is the force that propels the scooter forward and is equal to 300 N. The speed of the scooter is 30 m/s. Therefore, the power of the scooter is given by the following equation:

P = Fv = 300 N * 30 m/s = 9000 W

The current in the scooter can be calculated using the equation I = P/V, where I is the current, P is the power, and V is the voltage. In this case, the voltage of the scooter’s engine is 200 V. Therefore, the current in the scooter is given by the following equation:

I = P/V = 9000 W / 200 V = 45 A

The frictional force is not considered in the calculation because it is opposing the motion of the scooter, and therefore it is not contributing to the scooter’s power. Power is defined as the rate at which work is done, and the frictional force is not doing any work because it is not causing the scooter to move. Instead, the driving force of 300 N is doing the work of overcoming the frictional force and propelling the scooter forward. Therefore, the power of the scooter is equal to the driving force multiplied by the speed.

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Thank you for your explanation, it makes sense now!

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