Relative Motion

Q: A man is holding an umbrella at angle 30° with vertical with lower end towards himself, which is appropriate angle to protect him from rain for his horizontal velocity 10 m/s. Then which of the following will be true-

(A) rain is falling at angle 30° with vertical, towards the man

(B) rain may be falling at angle 30° with vertical, away from the man

(C) rain is falling vertically

(D) none of these

Click to See Solution :

Ans: (B)

Sol:

Let v = velocity of rain ; Hence Possible values of α are
-30º < α < 90º

Q: A ball is thrown horizontally from the top of a tower. What happens to the horizontal component of its velocity ?

(a)Increases

(b) Decreases

(c) Remains unchanged

(d) First decreases and then increases

Q: A swimmer is moving in a square course in a river. The flow velocity of the river is 3 ms^-1 and the velocity of swimmer relative to water is 5 ms^-1. The total distance travelled by the swimmer is 80 m.  Time taken by swimmer (in second) to complete the course is 22.5 n . Find the value of n.

Ans. 9

Q: Two particle P and Q are moving in gravity free space with their respective velocities $V_P = -\hat{i} + 2\hat{j} -2\hat{i}$  ms^-1 and $V_Q = -4\hat{i} + 2\hat{j} + 3\hat{k}$ ms^-1. At t = t_o , the separation between them is minimum. Find the value of 10 t_o .

Ans. 5