contestada

A driver in a car,originally moving 12.2 m/s, applies the brakes until the car comes to a stop. The car moves a distance of 36.5 m while braking. How much time did it take for the car to stop? Assume constant acceleration during braking.

Respuesta :

First we have to calculate the acceleration of the car,

[tex]a =\frac{u-v}{t}[/tex]

Here, u is initial velocity of the car and its value is given 12.2 m/s and v is final velocity of the car and it comes to stop, so its value zero.

[tex]a=\frac{0-12.2 m/s}{t} =\frac{-12.2 \ m/s}{t}[/tex].

As during the braking the acceleration is constant, from the kinematic equation,

[tex]s=ut + \frac{1}{2} a t^2[/tex]

Here, s is the distance traveled by the car during braking and its value is given 36. 5 m.

Substituting all the values in kinematic equation, we get

[tex]36.5 m =(12.2 m/s) t + \frac{1}{2} (- \frac{12.2 m/s}{t}) t^2 \\\\ 36.5 \ m = (12.2 \ m/s) t -(6.1 \ m/s) t \\\\\ t = \frac{36.5 m}{6.1 m/s} = 5.98 s[/tex]

Therefore, car will stop after 5.98 s.


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