CBSE Class 11-science - Relative Motion Videos

• What is relative velocity
• According to relative velocity formula we know that when two bodies move towards each other the relative velocity is equal to the sum of two velocities. Then why in calculating upstream where the direction of velocity of stream is against the direction of velocity of boat in still water we subtract the former from the latter even when they are opposite to each other? 
• A jet airplane traveling at the speed of 500 km/hr ejects its products of combustion at the speed of 1500 km/hr relative to the jet plane. What is the speed of the later with respect to an obserever on the ground? 
• Two ships A and B strat together from the same point. A sails 16 km/h towards east and B sails 20 km/h towards north. Find the relative velocity of B w.r.t A and distance between them after 5 hours.
• Two trains are moving in the opposite directions on parallel tracks, one with a velocity twice that of other. If the total length of the two trains is 480 ft and they take 3 seconds to cross each other, find their individual velocities.
• In a harbour, wind is blowing at the speed of 72 km/h and a flag on the mast of the boat anchored in the harbour along the N-E direction. If the boat starts moving at a speed of 51 km/h to the north, what is the direction of the flag on the mast of the boat.
• Two trains A and B of length 400 m each are moving on two parallel tracks with a uniform speed of 72 km/hr in the same direction, with A ahead of B.The driver of B decides to overtake A and accelerates by 1 m/s² . If after 50s, the guard of B just brushes past the driver of A, what was the original distance between them?
• Two cars A and B are moving with same speed 30 km/hr in same direction with car B 5 km behind the car A. Another car C moving in opposite direction crosses the two cars at an interval of 4 minutes. Find the speed of car C.
• Two cars A and B are travelling in same direction with speed v₁ and v₂ respectively (v_1 > v₂ ). When car A is d distance behind the car B, the brakes on A are applied, causing retardation . Show that to prevent a collision between A and B it is necessary that (v_1 > v₂ )² < (2d)
• A ship moves along equator to the east with velocity 30 km/hr. The southeastern wind blows at an angle of 60^o  to equator with velocity 15 km/hr. Find the wind velocity relative to ship and angle between the equator and the wind direction in reference frame fixed to the ship.

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