When you see a traffic light turn red, you apply the brakes until you come to a stop. Your initial speed was 12m/s . Assume constant deceleration. Suppose the car comes to rest in 36m .
How much times does this take?

Question

When you see a traffic light turn red, you apply the brakes until you come to a stop. Your initial speed was 12m/s . Assume constant deceleration. Suppose the car comes to rest in 36m .
How much times does this take?

anonymous · Answer

So you know initial velocity, final velocity, distance, and that it is uniformly accelerated motion. Do you have a formula that includes the given information along with the unknown, delta t?

anonymous · Answer

no i do not

anonymous · Answer

Alright, perhaps we need an intermediate step. Do you have enough information to calculate the acceleration?

anonymous · Answer

you can solve the problem using the equation$$\frac{ x }{t }=\frac{v+v_0}{2}$$

radar · Answer

Using the equation provided by alothman, I got a t of 6 seconds, is that reasonable for a speed of 43.2 km/hr and good brakes?

danjs · Answer

Given:$$v _{f} = 0~m/s$$$$v _{i}=12~m/s$$$$\Delta x = 36~m$$$$a = constant$$
Find: t [s]

danjs · Answer

Using the kinematic equations with constant acceleration, First calculate the constant acceleration from:
$$v _{f}^2=v _{0}^2+2a( \Delta x)$$
Use that value for acceleration, and calculate the time t [s] to stop the car
$$v _{f}=v _{o} + a*t$$

radar · Answer

Using the equations provided by DanJS, results in a value of 6 seconds for t.  For that speed which is 43.2 km/hr that seems reasonable.