Driving on asphalt roads entails very little rolling resistance, so most of the energy of the engine goes to overcoming air resistance. But driving slowly in dry sand is another story.
If a 1500 kg car is driven in sand at 5.0 m/s , the coefficient of rolling friction is 0.06. In this case, nearly all of the energy that the car uses to move goes to overcoming rolling friction, so you can ignore air drag in this problem.
a. What propulsion force is needed to keep the car moving forward at a constant speed?
b. What power is required for propulsion at 5.0 m/s ?
c. If the car gets 15 miles per gallon when driving on sand, what is the car's efficiency? One gallon of gasoline contains 1.4 x 10^8 J of chemical energy, one mile is 1609 m.

The answer to the given question would be as follows:

a). Propulsion Force

b). Power necessary for Propulsion

c). Car's efficiency %

a). Propulsion Force:

Given,

Weight of car = 1500 Kg

Speed = 5.0 m/s

Coefficient of rolling friction = 0.06

μ × ×

∵

b). Power necessary for Propulsion:

Given that,

Propulsion = 5 m/s

×

Now,

c). Capacity of the gallon = ×

1 mile = 1609 m

η

∵ η %

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a) , b) , c) .

Explanation:

a) Let assume that car travel on a horizontal surface. The equations of equilibrium of the car are:

After some algebraic handling, the following expression for the propulsion force is constructed:

b) The power require to move the car at a speed of 5 meters per second is:

c) The efficiency of the car is:

in physics zero. in muscle fatigue could be high

the ima (higher than 1m) will be greater than the ima with the height of 1m.