91Ó°ÊÓ

The velocity of air relative to the earth is 45 m/s. It is in 20 degree.

The sum of the plane's velocity relative to the air and the air's velocity relative to the earth equals the plane's velocity relative to the earth.

The velocity of the plane with respect to the earth:

$V_{pe}=V_{pa}+V_{ae}$

The component table will be as below:

Here we need to find the x component and the y component.

$$\begin{gathered} Xcomponent \\ {V}_x=V_i\cos \mathrm{θ} \\ {V}_x=\left(-V_{pa}\right)\cos \mathrm{θ} \\ {V}_x=\left(-V_{pa}\right)\cos 5^{°} \end{gathered}$$

$$\begin{gathered} Ycomponent \\ {V}_y=V_i\sin \mathrm{θ} \\ {V}_y=\left(-V_{pa}\right)\sin \mathrm{θ} \\ {V}_y=\left(-V_{pa}\right)\sin 5^{°} \end{gathered}$$

Hence, the velocity of air w.r.t to the earth component :

$\begin{array}{rcl}& & XComponent\\ V_x& =& V_i\cos \mathrm{θ}\\ V_x& =& \left(45\right)\cos {20}^{°}\\ V_x& =& 42.3\end{array}$

$\begin{array}{rcl}& & YComponent\\ V_y& =& V_i\sin \mathrm{θ}\\ V_y& =& \left(-45\right)\sin {40}^{°}\\ V_y& =& -15.4\end{array}$

Now we have given the angle of the resultant vector; hence

$$\begin{gathered} Xcomponent \\ {V}_x=V_{pe}\cos \mathrm{θ} \\ {V}_{pex}=\left(-V_{pe}\right)\cos {45}^{°} \\ Ycomponent \\ {V}_{pey}=V_i\sin \mathrm{θ} \\ {V}_y=\left(-V_{pe}\right)\sin {45}^{°} \end{gathered}$$

Hence, putting the value in the equation

$$\begin{gathered} \left(-V_{pa}\right)\cos {45}^{°}+42.3=\left(-V_{pe}\right)\cos {45}^{°}......\left(1\right) \\ Andequationtois: \\ \left(-V_{pa}\right)\sin {45}^{°}+\left(-15.4\right)=\left(-V_{pe}\right)\sin {45}^{°}......\left(2\right) \end{gathered}$$

After solving the above two equations, we can get the value of V_pa and V_pe.

Hence, V_pa= 63.5 m/s.

The velocity of the plane with respect to air is 63.5 m/s.

b) The speed of the plane relative to the earth should be

$$\begin{gathered} V_{pe}=\frac{V_{pa}\sin 5^{°}+15.4}{\sin {45}^{°}} \\ {V}_{pe}=29.6\raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$s$}\right. \end{gathered}$$

The velocity of the plane relative to the earth is 29.6 m/s.