Middle School

A driver in a car, originally moving at 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.

Answer :

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.


Final answer:

The car took 6 seconds to come to a stop.

Explanation:

To calculate the time it took for the car to stop, we can use the equation of motion:

vf² = vi² + 2ad

where:

  • vf is the final velocity (which is 0 m/s when the car comes to a stop)
  • vi is the initial velocity (12.2 m/s)
  • a is the acceleration (which is negative, since the car is decelerating)
  • d is the distance covered (36.5 m)

Plugging in the given values, we have:

0² = 12.2² + 2a(36.5)

Simplifying the equation:

0 = 148.84 + 73a

Solving for a:

a = -2.04 m/s²

Now, we can use the formula:

a = (vf - vi) / t

to find the time t it took for the car to stop.

Plugging in the values:

-2.04 = (0 - 12.2) / t

Simplifying the equation:

t = 6 seconds

Learn more about Calculating time of deceleration here:

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