The speed of one body with respect to the speed of another is called the relative speed of the first body to the second. Whereas the relative speed is measured in the frame in which an object is at rest or moving with respect to an absolute frame.

In this case, the resulting speed would be 75 km/hr; that is the speed of the aircraft with respect to an observer on the ground. Suppose that an aircraft travelling at a speed of 100 km/hr with respect to the air encounters a headwind at 25 km/hr.

However, if the two are travelling in opposite directions, then the relative speed of the one machine to the other is thus 60 ms-1 (see figure 1). We present the relative movement first in a single dimension, as two velocity vectors are simplified by having only two possible directions.

If we chose the positive direction east and the reference frame of the Earth, we can write the velocity of a train with respect to Earth as (vecv_TE)=10m/s(hati)east, with the subscripts TE denoting the train and Earth. If we choose east as the positive direction and Earth as the reference frame, then we can write the velocity of the train with respect to the Earth as (vec v _ TE ) = 10 m/s (hat i ) east, where the subscripts TE refer to train and Earth. In special relativity, V-B|AdisplaystylevecV_mathrmB|A is the speed at which an object or observer b is at the still frame relative to the other object or observer a.

Following are some of the multiple choice questions on the **Relative Velocity** with answers that will help the students in developing their knowledge.

## Relative Velocity MCQ

### 1. A 150 m long train moves towards south at a speed of 10 m/s. A sparrow flying at a speed of 5 m/s towards north crosses the train. What is the time taken by the sparrow to cross the train

### 2. A woman on a ten-speed bicycle travels at 9 m/s relative to the ground as she passes a little boy on a tricycle going in the opposite direction. If the boy is traveling at 1 m/s relative to the ground, how fast does the boy appear to be moving relative to the woman?

### 3. A dog is running at 12 m/s, a cat is running the opposite direction at 12 m/s. What is the magnitude of velocity of the cat relative to the dog?

### 4. A clown fish is swimming at 8 m/s, a sea anemone is standing still. What is the magnitude of velocity of the sea anemone relative to the clown fish?

### 5. Observers using different ___________________ may measure different velocities for an object in motion

### 6. The president’s airplane, Air Force One, flies at 250 m/s to the east (compared to the ground). The president visits the pilots in the cockpit. Then he walks to the back of the plane at 1 m/s. What is his speed relative to the ground?

### 7. A boat heading north crosses a wide river with a velocity of 10.00 km/h relative to the water. The river has a uniform velocity of 5.00 km/h due east. Determine the boat’s speed with respect to an observer on shore. (Hint: draw vector arrows - you should get a right triangle)

### 8. A train is moving at a velocity of 15 m/s East. A passenger at the back of a train throws a baseball with a speed of 15 m/s West. What is the velocity of the baseball relative to the ground? (In other words: how fast does a person on the ground see the ball move?)

### 9. A dog and a cat are about to fight, running towards each other, both at 12 m/s. What are their velocities relative to each other?

### 10. What method is used to find relative value for any vector quantity?

### 11. What does relative motion signify?

### 12. A body A is moving in North direction, while another body B is moving towards South. Velocity of A is greater than that of B. If North is taken as positive, which of the following relative velocities is positive?

### 13. An observer is sitting on a car moving with some constant velocity. The observer sees things around him, in the

### 14. A point A is placed at a distance of 7 m from the origin, another point B is placed at a distance of 10 m from the origin. What is the relative position of B with respect to A?

### 15. A car is moving with 20m/s velocity, another car is moving with a velocity of 50 m/s. What is the relative velocity of first car with respect to the second?

### 16. If two bodies are moving in opposite directions with non-zero velocities, which of the following statements is true?

### 17. The relative velocity of a body A with respect to a body B is 5 m/s. The absolute velocity of body B is 10 m/s. Both the bodies are moving in the same direction. What is the absolute velocity of body A

### 18. What is the correct formula for relative velocity of a body A with respect to B?

### 19. A body is moving with respect to a stationary frame, its motion can be called _____

### 20. X moves at a speed of 65 km/hr while Y who is behind X moves at a speed of 80 km/hr. What is the relative velocity of Y with respect to X?

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