Question

when to use relative velocity and when to use resulltant velocity concept?

1)Wind is blowing east and man makes his strokes perpendicular to waters surface....here we take resultant velocity
take a look at this question down here...it involves relative velocity of flag with respect to boat but why?

Answer 1

1)RESULTANT VELOCITY

2)RELATIVE VELOCITY
but why?

Answer 2

@Salini in the first case we take resultant velocity because the wind blowing affects the motion of the man swimming. Just like a boat travelling downstream or upstream

Answer 3

yes similarly movement of boat affect velocity of flag why arent we considering that as a resultant?

Answer 4

Second case we have to take relative velocity as with respect to boat the flag is stationary and fluttering . But with respect to a stationary frame of reference the flag is moving as the boat is moving. So wind will affect it differently

Answer 5

THis is the resultant velocity in the case, if a ball moves x direction and if the force applied in Y direction, the direction of the ball will be the resultant

Answer 6

can u explain it in a different way ash?
the relative velocity part

Answer 7

In your case, wind going towards x direction at 72kmph, boat moving at 51 kmph in Y+ direction, but the wind force acting on boat will be opposite to its motion. where Y- direction. Its relative to the direction og boat. So the direction would be x+y-. Its relative velocity.

Answer 8

Note velocity in both conditions are equal.

Answer 9

but the direction isnt that is the problem

Answer 10

Ya. Because the force acting on the flag is depends on the boat movement. Take if there's no wind, and boat travelling in Y direction means what would be the direction of the flag

Answer 11

Boat moving Y+ direction

Answer 12

-y direction flag moves

Answer 13

Ok. Now wind acting on the boat from X+ to X- direction. What is the resultant direction of the flag?

Answer 14

yeah i got it in the first case the river affects man's motion
while in 2nd both wind and boat affect flags motion
thank u for ur responses

Answer 15

Yeah. Thank You.