Applications relative to motion concept

Back to Home Page

Previous       Next

You may also Read

Applications relative to motion concept

In this case, the three velocities with which we have to deal are:

 Velocity of rain wrt ground;

 Velocity of man wrt ground;

 Velocity of rain wrt man From relative motion equation,

From this equation, we can construct a velocity vector diagram, which would be very helpful in solving the question.

The velocity vector diagram for a particular situation is shown in figure.

From sine law

Remember!

are not representing the length of triangles.

If in-air problems wind is blowing, then consider also the effect of wind blowing in the application.

River Problems

In this case, we have to deal with the following velocities:

 Velocity of swimmer/steamer/boat wrt river/water/stream.

 The velocity of swimmer/steamer/boat wrt ground.

From relative motion

For the situation shown in figure, a boat is crossing the river and it is heading (moving) along AP as shown,

then the time taken by boat to cross the river is,

and it will reach point Q due to river flow

The distance

is termed as drift.

 The velocity of plane wrt ground.

The relative motion equation would be

Aeroplane Problems

Here the following velocities are to be analyzed:

The velocity of plane wrt air.

The velocity of air wrt ground.

Conditions for Collision of Two Projectiles from Different Heights

Consider that two particles are projected from A and B with initial speed u1 and u2, respectively as shown in figure.

As the relative acceleration of 1 wrt 2 is zero, so particles will collide only and only 1 velocity of 1 wrt 2 would be along line AB. v12x = Component of velocity of 1 wrt 2 along X axis = u1

u12y = Component of velocity of 1 wrt 2 along Y axis = u1 sin ∝ 1  + u2 sin ∝2

Let velocity of 1 wrt 2 is making an angle β with +ve X-axis,
then

For collisions to take place, θ = β

Path of projectile as seen from another projectile 

Consider two particles A and B projected from the same point with initial speed u1 and u2 respectively as shown in figure.

So, the motion of one projectile as seen from another projectile will be a straight line.

Multiple Choice Questions


Back to Home Page

Previous       Next

You may also Read