Car Crashes: Friction to the Rescue?

📌 CONCEPT: Friction between the tyres and the road helps in stopping a vehicle due to the force of friction acting opposite to the direction of motion.

📐 RULE / FORMULA: To find the force of friction, we use the formula F = μN, where μ is the coefficient of kinetic friction and N is the normal force acting on the object.

💡 WORKED EXAMPLE: Given that the coefficient of kinetic friction (μ) is 0.5 and the normal force (N) is equal to the weight of the car (mg), we can calculate the force of friction as F = 0.5 * mg. Assuming the mass of the car is 1000 kg, the force of friction is F = 0.5 * 1000 * 9.8 = 4900 N. To determine if the car can be stopped within 20 m, we can use the equation of motion v^2 = u^2 + 2as, where v is the final velocity, u is the initial velocity, a is the acceleration, and s is the distance travelled.

⚠️ COMMON MISTAKE: Students often forget to consider the sign of the force of friction and assume it is always acting in the same direction as the motion, which can lead to incorrect calculations and conclusions.