Question

110-kg motorcycle and rider are traveling at 20 m/s. The rider notices a wreck ahead, applies the brakes, and manages to stop the car in 12 meters. Using work-energy, find the force of friction used to stop the car. (Pick the answer closest to the true value.)
A. 37,500 newtons
B. 3,375 newtons
C. 337 newtons
D. 450 newtons
E. 2,250 newtons

Answer 1

To solve this problem it is necessary to apply the concepts related to the Conservation of Energy. Basically the work done on the body is equal to the existing change in kinetic energy. Mathematically this can be expressed as

$W = KE$

$F*d = \frac{1}{2} mv^2$

Where,

F = Force

d = Distance

m = Mass

v = Velocity

Our values are given as

d = 12m

m = 110kg

v = 20m/s

Replacing to find the force we have that,

$F*d = \frac{1}{2} mv^2$

$F*12 = \frac{1}{2} (110)(20)^2$

$F = 1833N$

Choosing the closest value, the correct answer would be E.