Question
i. Pick out only the vector quantities from the following: Temperature, pressure, impulse, time, power, charge.
ii. Show by drawing a neat diagram that the flight of a bird is an example of composition of vectors.
iii. A man is travelling at $10.8 km h ^{-1}$ in a topless car on a rainy day. He holds his umbrella at an angle $37^{\circ}$ to the vertical to protect himself from the rain which is falling vertically downwards. What is the velocity of the rain? $\left[\right.$ Given $\cos 37^{\circ}=\frac{4}{5}$ ]

Answer

i. Impulse
ii. Flight of a bird. When a bird flies, it pushes the air with forces $F_1$ and $F_2$ in the downward direction with its wings $W_1$ and $W _2$. The lines of action of these two forces meet at point O . In accordance with Newton's third law of motion, the air exerts equal and opposite reactions $R_1$ and $R_2$. According to the parallelogram law, the resultant $R$ of the reactions $R_1$ and $R_2$ acts on the bird in the upward direction and helps the bird to fly upward.
Image
iii. $v _{ R }=10.8 km h ^{-1}=3 ms^{-1}$
Given: $\cos 37^{\circ}=\frac{4}{5} \therefore \tan 37^{\circ}=\frac{3}{4}$
But $\tan 37^{\circ}=\frac{v_R}{v_M}$ or $\frac{3}{4}=\frac{v_R}{3 m s^{-1}}$
or $v_R=\frac{9}{4}=2.25 ms^{-1}$

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