Time and Distance

• Speed v=s / t where s = Total distance t = Total time s = vt .

• The relative velocity of two bodies moving at velocities u and v(u>v) in the same direction is u - v.

• The relative velocity of two bodies moving in opposite directions is u + v.

• A train or a moving body of known length has to travel its own length in passing a lamppost or a fixed body of insignificant size.

• A train or a moving body must travel its own length plus the length of the stationary body in question, if the train or the moving body has to pass a stationary body i.e. a bridge, a railway platform etc.

• Motion downstream or upstream: Velocity of boat downstream = u + v Velocity of boat upstream = u - v Where "u" is the velocity of the boat in still waters and "v" is the velocity of the stream.

• If a man changes his speed in the ratio u : v, the corresponding ratio of times will be v : u .

• Average Speed:
• If an object covers equal distances at x km/hr and y km/hr, then Average Speed = 2xy/(x+y) In another way, Average speed = Distance / Total time