a 90kg car is speeding at 97km/h on a level road.determine the horizontal breaking force applied to stop it in

Question

a 90kg car is speeding at 97km/h on a level road.determine the horizontal breaking force applied to stop it in 67m.

Answer 1

force = mass x acceleration

therefore;

90 x 97 = 8730 K/j

Answer 2

If force is constant, the acceleration is constant. Under constant acceleration the velocity will linearly decrease. Then the average velocity traveling distance d is .5∆V. Since you are looking at the stopping distance, ∆V = 97km/h and the average velocity is half that. The time it takes to travel a distance d (=67m) is given by .5*∆V*t = d; then t = 2*d/∆V. The stopping distance is also given by d = .5*a*t^2. Substitute t from the first to get

d = .5*a*(2*d/∆V)^2 or d = .5*a*4*d^2/∆V^2; solve for a to get

a = (∆V^2)/(2*d). Use this a to get the force from f = m*a

Answer 3

the time to stop the car at 97km/hr is 2.49 sec

therefore, acceleration is around 10.82

so force is 973.8 KN