At an accident scene on a level road, investigators measure a car\'s skid mark t

Question

At an accident scene on a level road, investigators measure a car's skid mark to be 70 m long. It was a rainy day and the coefficient of friction was estimated to be 0.32. A. Use these days to determine the speed of the car when the driver slammed on (and locked) the brakes. B. Why does the car's mass not matter? Since the work done by the friction does not depend on mass. Since the change in kinetic energy and the work done by friction do not depend on mass. Since both the change in kinetic energy and the work done by friction are proportional to the mass. The mass cancels out of the equation. At an accident scene on a level road, investigators measure a car's skid mark to be 70 m long. It was a rainy day and the coefficient of friction was estimated to be 0.32. A. Use these days to determine the speed of the car when the driver slammed on (and locked) the brakes. B. Why does the car's mass not matter? Since the work done by the friction does not depend on mass. Since the change in kinetic energy and the work done by friction do not depend on mass. Since both the change in kinetic energy and the work done by friction are proportional to the mass. The mass cancels out of the equation. A. Use these days to determine the speed of the car when the driver slammed on (and locked) the brakes. B. Why does the car's mass not matter? Since the work done by the friction does not depend on mass. Since the change in kinetic energy and the work done by friction do not depend on mass. Since both the change in kinetic energy and the work done by friction are proportional to the mass. The mass cancels out of the equation.

Explanation / Answer

A)Let m is the mass of the car.

let fk is the kinetic friction acting on the car.

Net force acting on car = -fk

m*a = -mue_k*N

ma* = -mue_k*m*g

a = -mue_k*g

= -0.32*9.8

= -3.136 m/s^2

let u is the initial speed and final speed.

v = 0

u = ?

Apply, (v^2 - u^2) = 2*a*d

(0^2 - u^2) = 2*(-3.136)*70

-u^2 = -439.04

u = sqrt(439.04)

= 20.95 m/s

B)

Since both the change in kinetic energy and the work done by friction are proportional to the mass. The mass cancels out of the equation.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.