Question

On a road a sports car weighing 4000N must move while it is stopped, the coefficients of the car and the ground are 0.4 and 0.3. Calculate the horizontal force needed (a) to start the car moving and (b) to keep the car moving at a constant speed.

Answer 1

To start a sports car weighing 4000N, a force of 1600N is needed to overcome static friction, while a force of 1200N is needed to keep it moving at a constant speed, overcoming kinetic friction.

Step-by-step explanation:

When determining the horizontal force needed to start a car moving and to keep it moving at a constant speed, we must consider the coefficients of static and kinetic friction, respectively. (a) To start moving a sports car that weighs 4000N, one needs to overcome static friction. This requires a force equal to the product of the car's weight and the coefficient of static friction (μs), which is given as 0.4. Therefore, the force needed is Fstart = μs × weight = 0.4 × 4000N = 1600N. (b) To keep the car moving at a constant speed, only the kinetic friction needs to be overcome, which has a coefficient (μk) of 0.3. Hence, the force required in this case is Fconstant = μk × weight = 0.3 × 4000N = 1200N.