what is a race car's acceleration if its velocity changes from 0 m/s to 40 m/s in 4 seconds.

Question

whpalmer4 · Answer

$$v_f - v_i = a t$$where $v_i$ is initial velocity, $v_f$ is final velocity, $a$ is (constant) acceleration, and $t$ is time

anonymous · Answer

so 10 m/s

whpalmer4 · Answer

Not quite. Right number, wrong unit, thus wrong answer...

whpalmer4 · Answer

As $v_i=0$, $$v_f = at$$$$a = \frac{v_f}{t}$$
$$a = \frac{ 40\frac{\text{ m}}{\text{ s}} }{4 \text{ s}} = 10 \frac{\text{m}}{\text{s}^2}$$

whpalmer4 · Answer

acceleration always has dimensions of $$\frac{\text{[length]}}{\text{[time]}^2}$$

anonymous · Answer

Ahhh okay

whpalmer4 · Answer

Always do your physics problems with the units.  If the units don't behave properly, you've set the problem up wrong, or muffed a unit conversion, and your answer is undoubtedly wrong.

anonymous · Answer

Okay so just 10 m/s^2

whpalmer4 · Answer

Yes, that is correct.  Coincidentally, that's about the same acceleration as gravity on the earth's surface (9.81 m/s^2), so you'll sometimes see that referred to as "1 g"

anonymous · Answer

Thank you