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
Oct 29, 2015

I found 56m/s

Explanation:

Here you can use the cinematic relationship:

color(red)(v_f=v_i+at)

Where:
t is time,
v_f is the final velocity,
v_i the initial velocity and
a acceleration;
in your case:
v_f=80-2*12=56m/s

Oct 29, 2015

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

Explanation:

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

2m/s²=2m/s/s

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

80-24=56