> 1). Speed, v = s/t. where s = Total distance, t = Total time 2). The relative velocity of two bodies moving at velocities u and v (u>v) in the same direction is (u – v). 3). The relative velocity of two bodies moving in opposite directions is (u + v). 4). A train or a moving body of known length has to travel its own length in passing a lamp post or a fixed body of insignificant size. 5). 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. 6). 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. 7). If a man changes his speed in the ratio u : v, the corresponding ratio of times will be v : u ### FORMULAS FOR Time & Work PROBLEM ### 1. If a person can do a piece of work in ‘m’ days, he can do 1/m of the work in 1 day. 2. If the number of persons engaged to do a piece of work be increased (or decreased) in a certain ratio the time required to do the same work will be decreased (or increased) in the same ratio. 3. If A is twice as good a workman as B, then A will take half the time taken by B to do a certain piece of work. 4. Time and work are always in direct proportion. 5. If two taps or pipes P and Q take ‘m’ and ‘n’ hours respectively to fill a tank, then the two pipes together fill (1/m + 1/n) part of the tank in 1 hour and the entire tank is filled in mn/(m+n) hours.
Posted on: Tue, 28 Oct 2014 19:04:20 +0000
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