What is the frictional force acting on a car at 120 mph with a 30 hp engine?

[KatieLynn]

Homework Statement

When an automobile moves with constant velocity, the power developed is used to overcome the frictional forces exerted by the air and the road. If the engine develops 30 hp, what total frictional force acts on the car at 120 mph?

Homework Equations

1hp = 746W
1mile-1609m
work=force*distance
power= work/time

The Attempt at a Solution

30hp= 22380w
120mph= 53.6448m/s
I'm really not sure where to go from there, you need to end up with force which is Newtons, don't you need a mass in kg to for that?

 

[rl.bhat]

Power = Force*velocity.

 

[KatieLynn]

so can you just multiply 22380w and 53.6448m/s, or do you have to change the watts to another unit?

 

[KatieLynn]

oopps you have to divide them actually right?

 

[rl.bhat]

Yes. No need to change anything.