Relative velocity is the velocity of one object as measured from the reference frame of another object.
How fast something seems to move depends on who is watching.
Showing a random 20 of 50 problems.
Example 1
medium
Train A at 25 m/s east passes train B at 15 m/s east on a parallel track. Velocity of B in A's frame?
Example 2
medium
Is relative velocity a scalar or a vector quantity?
Example 3
medium
A swimmer swims 2 m/s relative to water across a current of 1.5 m/s at right angles. Find swimmer's ground speed.Swimmer 2 m/s + current 1.5 m/s → ground speed 2.5 m/s
Example 4
easy
Two cars approach head-on: A at 30 m/s east, B at 20 m/s west. Find their closing speed.
Example 5
challenge
In still air a plane flies 250 m/s. It must fly due north while a 70 m/s east wind blows. Find its ground speed due north (round to nearest m/s).Plane heading + eastward wind → resultant due north at 240 m/s
Example 6
medium
A plane has airspeed 200 m/s east. A 50 m/s wind blows from north to south. Find ground velocity (magnitude and direction).Plane 200 m/s east + wind 50 m/s south → ground velocity ≈ 206 m/s at 14° south of east
Example 7
medium
A jet flies 200 m/s east into a 30 m/s east headwind... actually the wind blows west at 30 m/s. Find the ground speed.
Example 8
easy
Car A moves 20 m/s east, car B moves 12 m/s east. Find A's velocity relative to B.
Example 9
easy
Two runners side by side at 4 m/s. Velocity of one relative to the other?
Example 10
challenge
From a car moving 25 m/s east, a passenger throws a ball 15 m/s east relative to the car. A pedestrian on the ground observes the ball. Find the ball's ground velocity. If the car then decelerates at 2 m/s2, does the ball's ground velocity change after release?Car 25 m/s east + ball thrown 15 m/s east (relative to car) → ball ground velocity 40 m/s east
Example 11
medium
A swimmer moves 1.5 m/s relative to water; the river current is 2.0 m/s. Swimmer heads directly across (perpendicular to current). Find ground speed.Swimmer 1.5 m/s + current 2.0 m/s → ground speed 2.5 m/s
Example 12
hard
A boat must cross a 100 m-wide river to a point directly opposite. Boat speed relative to water is 5 m/s; current is 3 m/s. At what angle upstream must the bow point, and what is the crossing time?Boat upstream heading + current → resultant due north; crossing time = 25 s
Example 13
easy
Two cars approach head-on: A at 25 m/s east, B at 15 m/s west. Find their closing speed.
Example 14
challenge
Two trains 1000 m apart approach: A at 30 m/s, B at 20 m/s (toward each other). When do they meet?
Example 15
easy
A boat moves 4 m/s east relative to water; water moves 3 m/s west. Find the boat's speed relative to ground.
Example 16
easy
Why must direction be tracked when combining velocities?
Example 17
medium
Two cars approach head-on: A at 18 m/s east, B at 12 m/s west, initially 300 m apart. When do they meet?
Example 18
medium
Person walks 2 m/s forward on a train going 18 m/s; another walks 2 m/s backward. Find each person's ground velocity.
Example 19
hard
Two cyclists ride toward each other, each at 4 m/s, initially 200 m apart. A bee flies 8 m/s between them until they meet. Find total bee distance.
Example 20
easy
A walkway moves 1.2 m/s east. A person walks 0.8 m/s east on it. Speed relative to ground?