# Relative Velocity

## Trending Questions

**Q.**

Pilar is playing with a motorized toy boat.

She puts the boat in a lake and it travels $400$m at a constant speed.

On the way back to Pilar, the boat travels the same route at the same speed for $2$ minutes, and then Pilar uses the remote control to increase the boats speed by $10$ m/min.

So the return trip is $60$ seconds faster. How long does the return trip take?

**Q.**Two particles, one with constant velocity 50 m s−1 and the other with uniform acceleration 10 m s−2, start moving simultaneously from the same place in the same direction. They will be at a distance of 125 m from each other after

- 3 s
- 5(1+√2)s
- 10 s
- 10(√2+1)s

**Q.**

A $200m$ long train crosses a $1400m$long bridge with a uniform speed of $72km/h$ . Calculate the time taken by the train to cross the bridge?

**Q.**

You are walking towards India Gate. Is India Gate at rest with respect to you or in motion with respect to you?

**Q.**A train is running at a speed of 72 km/hr. A boy runs inside the train in same direction (as that of train) with a speed of 10 km/hr with respect to the train. Find the velocity of boy as seen from the ground.

- 62 km/hr along the direction of motion of train
- 72 km/hr opposite to direction of motion of train
- 82 km/hr along the direction of motion of train
- None of these

**Q.**A train is running at a speed of 72 km/hr. A boy runs inside the train in same direction (as that of train) with a speed of 10 km/hr with respect to the train. Find the velocity of boy as seen from the ground.

- 62 km/hr along the direction of motion of train
- 72 km/hr opposite to direction of motion of train
- 82 km/hr along the direction of motion of train
- None of these

**Q.**Find the time after which the two balls will collide.

- 4s
- 5s
- 6s
- 8s

**Q.**The distance between two particles is decreasing at the rate of 6msec. If these particles travel with same speeds as in previous case and in the same direction, then the separation increase at the rate of 4msec. The particles have speeds as

- 5msec;1msec
- 4msec;1msec
- 4msec;2msec
- 5msec;2msec

**Q.**Two cars are moving in the same direction with a speed of 30 kmph. They are seperated from each other by 5 km. Third car moving in the opposite direction meets the two cars after an interval of 4 minutes. What is the speed of the third car?

- 30 kmph
- 35 kmph
- 40 kmph
- 45 kmph

**Q.**An object A is moving with 10 m/s and B is moving with 5 m/s in the same direction as shown. Initially A is 100 m behind B as shown. Find the time taken by A to meet B

- 18 s
- 16 s
- 20 s
- 17 s

**Q.**Two trains each having a speed of 30 kmph are headed at each other on the same straight track. A bird that can fly at 60 kmph flies off from one train when they are 60 km apart and heads directly for the other train. On reaching the other train, it flies directly back to the first and so forth. How many trips can the bird make from one train to the other before the crash. Also find the total distance that the bird travels.

- trips=∞, distance=60 km
- trips=30, distance=30 km
- trips=5, distance=60 km
- trips=5, distance=30 km

**Q.**A man is walking on a road with a velocity 3 km/hr. Suddenly rain starts falling. The velocity of rain is 10 km/hr in vertically downward direction. The relative velocity of the rain with respect to man is -

- √13 km/hr
- √7 km/hr
- √109 km/hr
- 13 km/hr

**Q.**A ship is travelling due east at 10 km/hr. Another ship heading 30∘ east of north is always due north from the first ship. The speed of the second ship in km/hr is

- 20√2
- 20√32
- 20
- 20√2

**Q.**An express train is moving with a velocity v1. Its driver finds another train is moving on the same track in the same direction with velocity v2 (v2<v1). To escape collision, driver applies a retardation a on the train. The minimum time to escape the collision is

- (v1−v2)a
- (v21−v22)2
- (v2)a
- (v1+v2)a

**Q.**A thief is running away on a straight road in a jeep moving with a speed of 9 ms−1. A policeman chases him on a motor cycle moving at a speed of 10 ms−1. If the instantaneous separation of the jeep from the motor cycle is 100 m, how long will it take for the policeman to catch the thief?

- 1 s
- 19 s
- 90 s
- 100 s

**Q.**While you are travelling in a car on a straight road at 90 km/h, another car passes you in the same direction; its speedometer reads 120 km/h. What is your velocity relative to the other driver? (in km/h)

- 30
- −30
- 210
- −210

**Q.**A particle A is moving with a speed of 10 m/s towards right and another particle B is moving at speed of 12 m/s towards left. Find their velocity of approach.

- −2 m/s
- 10 m/s
- 12 m/s
- 22 m/s

**Q.**A boat running upstream takes 7 hr to cover a certain distance, while it takes 4 hr to cover the same distance running downstream. What is ratio of the speed of boat in still water to the speed of water current?

- 11:3
- 3:2
- 7:3
- Can't be determined

**Q.**A pump is pumping water from the well at a depth of 8 m at the rate of 5 kg per second. The speed of water coming out is 10m/s. The power of the pump is [g=10m/s2]

- 550 W
- 400 W
- 800 W
- 650 W

**Q.**A boat running upstream takes 7 hr to cover a certain distance, while it takes 4 hr to cover the same distance running downstream. What is ratio of the speed of boat in still water to the speed of water current?

- 11:3
- 3:2
- 7:3
- Can't be determined

**Q.**Velocity of the boat with respect to river (vb/r) is 10 m/s. It passes the river of width 36 m and reaches opposite shore at point R shown in the figure. If the velocity of the river is 3 m/s, find the time of the trip and drift of the boat.

- (6 s, 66 m)
- (6 s, 60 m)
- (4.5 s, 49.5 m)
- (6 s, 49.5 m)

**Q.**Two particles, one with constant velocity 50 m s−1 and the other with uniform acceleration 10 m s−2, start moving simultaneously from the same place in the same direction. They will be at a distance of 125 m from each other after

- 3 s
- 5(1+√2)s
- 10 s
- 10(√2+1)s

**Q.**A motorboat covers a given distance in 6 hours moving downstream on a river. It covers the same distance in 10 hours moving upstream. The time it takes to cover the same distance in still water is

- 9 hours
- 7.5 hours
- 6.5 hours
- 8 hours

**Q.**Train A travelling at 60 km/h overtakes another train B travelling at 42 km/h. Assuming each train to be 50 m long and initially train A to be just behind the train B, the total road distance used for the overtake is closest to

- 180 m
- 383 m
- 343 m
- 250 m

**Q.**An express train is moving with a velocity v1. Its driver finds another train is moving on the same track in the same direction with velocity v2(v2<v1). To escape collision, the driver applies a retardation a on the train. The minimum time to escape the collision is

- (v1−v2)a
- (v21−v22)2
- (v2)a
- (v1+v2)a

**Q.**A police jeep is chasing with, velocity of 45 km/h a thief in another jeep moving with velocity 153 km/h. Police fires a bullet with muzzle velocity of 180 m/s. The velocity it will strike the car of the thief is

- 150 m/s
- 27 m/s
- 450 m/s
- 250 m/s

**Q.**Two particles start simultaneously from points A and B as shown in the figure. Then what is the minimum distance between them?

- 5 m
- 10 m
- 15 m
- 20 m

**Q.**A man can row a boat with 4 km/hr in still water. If he is crossing a river where the current is 2 km/hr, how long will it take him to row 2 km upstream and then back to his starting point?

- 34 hr
- 32 hr
- 23 hr
- 43 hr

**Q.**A 120 m long train is moving in a direction with speed 20 m/s. A train B moving with 30 m/s in the opposite direction and 130 m long crosses the first train in a time

- 6 s
- 36 s
- 38 s
- None of these

**Q.**An express train is moving with a velocity v1. Its driver finds another train is moving on the same track in the same direction with velocity v2 (v2<v1). To escape collision, driver applies a retardation a on the train. The minimum time to escape the collision is

- (v1−v2)a
- (v21−v22)2
- (v2)a
- (v1+v2)a