Question

What is the braking force? Bear in mind Newton’s laws of motion ;) deacleration is 8.23 m/s^2    over 30 m    no mass given for car. speed of car before brakeing is 80kmh

13.45 kN

17,941.4 N

17,941 kN

13,451 N

Answer 1

KINETICS is the branch of classical mechanics that deals with the relationship between causes of motion such as forces and torques and the motion itself.

Where as
KINEMATICS describes the motion of bodies and systems of bodies without considering the mass of each or the forces that caused the motion.

So the only thing that differentiates a kinetics problem from a kinematics problem of the same information is the inclusion of a mass which ,when acted upon by a force produces acceleration.

So Effect of Force (acceleration) and Mass
of the body are inseparable for a kinetics problem.

Unless if you are talking about the ratio (F/m) which is the only case when mass is not needed but the result comes to acceleration anyway. Because of NEWTON'S SECOND LAW OF MOTION
F=m*a

Hence I'll try to solve it solve it as a kinematics problem and try to find out the unknowns.

Given that the car decelerates at
a=8.23 m/s^2 ,over a distance of s= 30 m
Speed of the car before braking
u=80 kmph=80*5/18 m/s=22.223 m/s

Now if the velocity after the body travels for 30 m is v

By using work energy theorem,
Change in kinetic energy of the car
=Work done by the brakes to decelerate the car

1/2*m*v^2-1/2*m*u^2=F.s=m*a*s
s=(v^2-u^2)/(2*a)
Upon rearrangement,the equation changes to v^2=u^2+2*a*s
v=(22.223^2+2*(-8.23)*30)=0.165 m/s

Which means that the body didn't stop after travelling the 30 m

Time taken to travel 30 m is T=(v-u)/a
T=(0.165-22.223) (m/s)/-8.23 (m/s^2)
T=2.68 sec

But this is not the time of stop as there is still some momentum left in the car (m*v)

You can calculate the stopping time and distance by taking the final velocity as ZERO.

If you still want to calculate Braking Force is in it's true sense then substitute a statistical value of average weight of a car in Newton's second law to get the force.

I'm solving this problem with the sole purpose to let you know that mass of the car is needed to solve this problem and if there is any other way through this I definitely want to know.

IF YOU LIKED MY ANSWER TO YOUR QUESTION, PLEASE SUPPORT ME WITH A THUMBS UP, FEEL FREE TO POST A COMMENT OR ANY CORRECTION IN THE THEORIES I EMPLOYED .T.H.A.N.K.Y.O.U.

Disclaimer: I claim no ownership to any content mentioned above as mine. I give full credit to the original authors of the content and that I'm using it to better the quality and effectiveness of my answer which your content brings in. Thank you.