Two cars travel at the same speed of 105 km/h

[physics_kills]

Two cars travel at the same speed of 105 km/h. One of the cars, a sleek sports car, has a motor that delivers only 35 kW of power at this speed. The other car's motor needs to produce 65 kW to move the car at this speed. Forces exerted from air resistance cause the difference.

A) For each car, list the external horizontal forces exerted on it, and give the cause of each force. Compare their magnitudes.
B) According to Newton's third law of motion, each car exerts forces. What are the directions of these forces?
C) Calculate the magnitude of the forward force exerted by each car on the air.
D) The car engines did work. Where did the energy they transferred come from?


I really have no clue where to begin when solving this problem, and I'd love some help if anyone knows how to do this! Thank you sooo much!

 

[fatra2]

Hi there,

Probably the best tip one can give you is to make a drawing of the situation. It does not have to be pretty (we are not artist, but doing physics), just explaning the situation. Once you have you two cars drawn, then imagine what are the forces acting upon them. The rest should come easily.

Cheers

 

[kerimek]

A) The external horizontal forces exerted on each car are the driving force from the engine and the air resistance force. The cause of the driving force is the motor of the car, while the cause of the air resistance force is the air particles colliding with the car as it moves. The magnitude of the air resistance force will be greater for the car with the weaker motor, as it needs to exert more power to maintain the same speed.

B) According to Newton's third law, for every action, there is an equal and opposite reaction. Therefore, each car will exert a force on the air in the opposite direction of its motion.

C) The magnitude of the forward force exerted by each car on the air can be calculated using the formula F = ma, where F is the force, m is the mass of the air being displaced, and a is the acceleration of the air. Since both cars are traveling at the same speed, their accelerations are the same. However, the car with the weaker motor will need to displace more air to maintain the same speed, so it will exert a greater force on the air.

D) The energy transferred by the car engines comes from the fuel they burn. The fuel contains chemical energy, which is converted into kinetic energy (energy of motion) by the car's engine. This kinetic energy is then transferred to the wheels, which move the car forward. Some of this energy is also used to overcome the air resistance force and maintain the car's speed.