A car moves with a speed of 80 m/s. If the driver used the brakes to decrease the speed, so it decreases by 2 m/sec^2. What is its speed after 12 seconds from using the brakes?

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A car moves with a speed of 80 m/s. If the driver used the brakes to decrease the speed, so it decreases by 2 m/sec^2. What is its speed after 12 seconds from using the brakes?

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Answer 1 · 2015-10-29T18:01:59

I found $56 \frac{m}{s}$ $56m/s$

Explanation:

Here you can use the cinematic relationship:

$v_{f} = v_{i} + a t$ $color(red)(v_f=v_i+at)$

Where:
$t$ $t$ is time,
$v_{f}$ $v_f$ is the final velocity,
$v_{i}$ $v_i$ the initial velocity and
$a$ $a$ acceleration;
in your case:
$v_{f} = 80 - 2 \cdot 12 = 56 \frac{m}{s}$ $v_f=80-2*12=56m/s$

Answer 2 · 2015-10-29T18:07:34

The car's speed after twelve seconds of using brakes is $56$ $56$ m/s

Explanation:

If the car's acceleration due to braking is $2$ $2$ m/s², that means that every second, the car's speed decreases by $2$ $2$ m/s:

$2$ $2$ m/s² $= 2$ $=2$ m/s/s

Therefore, if the car's speed is $80$ $80$ m/s when the brakes are used, its speed is $78$ $78$ m/s one second later and, after $12$ $12$ seconds, its speed will be $12 \cdot 2 = 24$ $12*2=24$ m/s lower.

$80 - 24 = 56$ $80-24=56$

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A car moves with a speed of 80 m/s. If the driver used the brakes to decrease the speed, so it decreases by 2 m/sec^2. What is its speed after 12 seconds from using the brakes?

2 Answers

Explanation:

Explanation:

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