Question

Conceptual question 

a) When we see a car go by on the highway at 120 miles / h we exclaim things like "That
car is really fast! ”, although in reality it is going with constant speed. Why if the
accelerator pedal is too tight, the car is not accelerated? Explain using the laws of
Newton.
b) Many times we think that what makes the car move is its engine. However, for very
powerful the motor (the energy it delivers per unit of time), the car cannot
move if you are on a mudrack, or on a puddle of fat. Is it the engine, or is the road what
what accelerates the car? Explain using Newton's laws.

Answer 1

(a) There are external opposing forces acting on the car which makes the total force on the car as zero. This causes the car to move at constant velocity. The force due to acceleration of the car is balanced by the frictional and air drag forces. These opposing forces are the reason why the car is moving at a constant speed (due to external force as zero).

(b) Here in this case, what makes the car move is the frictional force which acts between the tyre and the road of the wheel. Until there is enough friction there will be always slips, which is the case for mud-tracks where the friction between tyre and ground is less and the energy is not properly utilised to accelerate the car.