Question

A bird takes off at an angle of 30° to the ground with a velocity of 6 m/s. Which expression shows the bird’s height after 2 seconds?

Answer 1

A vector at an angle of 30° can be thought as the sum of a horizontal and a vertical vector, which we will call $v_h,v_v$.

In particular, you have

$v = v_{h}+v_{v}$

and moreover, we have

$v_{h} = v\cos(\alpha),\quad v_{v}=v\sin(\alpha)$

So, if we are only interested in the vertical component of the bird's flight, we have to consider a velocity of

$6\sin(30) = 6\cdot 0.5 = 3$

This means that the bird rises with a constant speed of 3m/s, and thus his equation is

$h = 3t$

where $h$ is the height in meters and $t$ is the time in seconds