# Question #81be9

##### 1 Answer

#### Explanation:

The cool thing to notice here is that you can solve this problem without using any equations; all you have to do here is to use the *definition* of acceleration.

As you know, an object's **acceleration** tells you how the velocity of said object is changing in time.

#"acceleration" = "change in velocity"/"chaneg in time" = (Deltav)/(Deltat)#

More specifically, acceleration represents a measure of how fast the velocity of an object is changing **per second**.

In your case, the plane has an acceleration of

#"4 m s"^(-2) = "4 m s"^(-1) * "s"^(-1) = "4 m/s"/"1 s" color(white)(color(blue)( -> " change in velocity")/(color(blue)(->" per second"))#

This is equivalent to saying that the velocity of the place **increases** by **with every passing second**. Since you know that the plane is accelerating for **increase** by

#40 color(red)(cancel(color(black)("s"))) * "4 m s"^(-1)/(1color(red)(cancel(color(black)("s")))) = "160 m s"^(-1)#

If you assume that the plane is starting from rest, i.e. with an initial velocity equal to

#v_"takeoff" = "0 m s"^(-1) + overbrace("160 m s"^(-1))^(color(blue)("increase due to acceleration")) = color(darkgreen)(ul(color(black)("160 m s"^(-1))))#

I'll leave the answer rounded to two **sig figs**, but keep in mind that you only have one significant figure for your data.