Have i looked at the signal?

Classical Mechanics Level 2

You are driving along the street at the speed limit (35mph) and 50 meters before reaching a traffic light you notice it becoming yellow. You accelerate to make the traffic light within the 3 seconds it takes for it to turn red. What is your speed as you cross the intersection? Assume that the acceleration is constant and that there is no air resistance (answer in mph)

40 450 data is wrong 150

1 solution

Nelvson Shine
Mar 5, 2014

so from the data we know that :

$v_0$ is 35 mph = 15.645 m/s

s ( distance ) = 50 m

t = 3 s

from the equation $s = v_0 t + \frac{at}{2}$ , there we can find the acceleration

$a = 2(s - v_0 t) / t^2$

$a = 2(50 - 15.645*3) / 9$

$a = .6811 m/s$

So we have, acceleration, and $v_0$ . Then we can get the final velocity (v)

v = $v_0$ + at

$v = 15.6 + 6.811*3$

$v = 17.64 m/s$

The answer is 17.64 m/s. Or using a converter, it's about 40 mph

for the problem setter, maybe you should put a converter ( from mph to m/s ). some of us don't use the mph system

Nelvson Shine - 7 years, 3 months ago

Have i looked at the signal?

1 solution

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