Relative Motion

Questions & Answers

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

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

Ans: (c)

Sol: As there is No acceleration in horizontal direction hence the horizontal component of its velocity remains unchanged .

A swimmer is moving in a square course in a river. The flow velocity of the river is 3 m/s and the velocity of swimmer relative to water is 5 m/s….

Q: A swimmer is moving in s 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.

Numerical

Ans. 9

Two particle P and Q are moving in gravity free space with their respective velocities V_p = -i + 2j -2k  ms-1 and V_p = -4i + 2j + 3k  ms-1. At t = to , the separation between them is minimum. Find the value of 10 to .

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 = to , the separation between them is minimum. Find the value of 10 to .

Ans. 5

A swimmer is approaching the shore with a speed of 5√3 m/s  . At the instant when it is at a distance of 30√3 m from the shore, he projects a ball at an elevation of 30° for it to just reach the shore. The speed of stone relative to swimmer is 5x ms-1. Find the value of x.

Q: A swimmer is approaching the shore with a speed of 5√3 m/s  . At the instant when it is at a distance of 30√3 m from the shore, he projects a ball at an elevation of 30° for it to just reach the shore. The speed of stone relative to swimmer is 5x ms-1. Find the value of x.

Ans. 4

Assume ground as XY-plane and vertically upward as Z-axis. The velocity of an aeroplane is 3i + 4 j + 5 k  . A car is moving on ground as such aeroplane is always above the car. At t = 0, both starts from origin of coordinate system. Choose the correct statement(s).

Q: Assume ground as XY-plane and vertically upward as Z-axis. The velocity of an aeroplane is $3 \hat{i} + 4 \hat{j} + 5 \hat{k}$ . A car is moving on ground as such aeroplane is always above the car. At t = 0, both starts from origin of coordinate system. Choose the correct statement(s).

(a) The velocity of car is $3 \hat{i} + 4 \hat{j} $

(b) The equation of path of car is $y = \frac{4}{3}x $

(c) The velocity of aeroplane seen by an observer in car is $5\hat{k}$

(d) None of the above

Ans: (a),(b),(c)