- #1

ddobre

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## Homework Statement

An electric car (mass 1560 kg) draws power from a set of 24 batteries. Each battery supplies 12 V, with storage 95 A·h. During a test of the vehicle, it is driven at exactly 45 km/h on a level road while experiencing a friction force of 240 N.

(a) What is the horsepower required during this test?

(b) Neglecting all other forms of energy loss (e.g. inefficiencies, acceleration), how many kilometers can the car travel before the batteries need to be recharged?

## Homework Equations

P = A*V

1hp = 746w

P = F*v(velocity)

## The Attempt at a Solution

The first thing I did was add up all the batteries voltages. Next I multiplied that value by the 95A*h rating to get P(watts) = 27360w*h. Next, I converted the speed from km/h to m/s: 12.5 m/s. Lastly, I tried finding the power of the frictional force on the car via P = F*v, (P = 240N * 12.5 m/s), and got 3000w. As a way of relating things, I wrote 27360w in terms of hp: 36.68hp. The part I am confused about is how I should be relating the frictional force to the horsepower required, and I'm also a little confused about the units of power I calculated for the frictional force. I have not thought about part b) yet. Any advice?