Un auto de 1000 kg que lleva una velocidad de 72 km/h se detiene en una distancia de 100 metros cuando se le aplican los frenos. (a) ¿Cuál es la fuerza constante producida por los fre. Nos? (b) Con esta fuerza, ¿cuál seria la distancia de frena do si la velocidad hubiera sido de 36 km/h?

a)    F = 2000 N , B)   x = 25 m

Explanation:

a) To solve this exercise we can use the relationship between work and kinetic energy

          W = ΔK

The job is

           W = -F x

the negative sign is because the force of the brakes is contrary to the movement

as the car stops its final kinetic energy is zero

           K = ½ m v²

let's substitute

         - F x = 0 - ½ m v²

            F = ½ m v² / x

Let's reduce the magnitudes to the SI system

           v = 72 km / h (1000m / 1km) (1 h / 3600 s) = 20 m / s

let's calculate

          F = ½ 1000 20²/100

          F = 2000 N

b) x = ½ mv2 / F

let's slow down to the SI system

         v = 36 km / h = 10 m / s

let's calculate

             x = ½ 1000 10²/2000

             x = 25 m

a) electrical > light, sound, and thermal< < < <

) the mechanical energy of the firefighter moving.< < < < a) electrical > light, sound, and thermal< < < <

c) both a and b.

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.