Speed: The speed of an object is the distance covered by it in unit time. We can write it as follows:
Speed can be expressed in any of the following units… it could be Kilometers / Hour, Meters / Seconds, Feet / Seconds, Miles / Hours, etc.
Speed can be classified into two types:
Uniform Speed and Variable Speed: If the object covers equal distance in equal intervals of time, then it is said to be traveling with uniform speed. If not, its speed is said to be variable.
Average Speed: It is calculated by using the following formula:
Relative Speed: The speed of one object with respect to the speed of another object is called relative speed.
Rules of finding the Relative Speed
- If the two objects are moving in the same direction at a speed say
km/hr and
km/hr, then their relative speed
km/hr, where
- If two objects move in opposite directions at speeds of
km/hr and
km/hr respectively, then their relative speed is
km/hr
Problems on Trains
- Time taken by a train
meters long in passing a signal pole or a point or a man standing = Time taken by the train to cover
meters
- Time taken by a train
meters long in passing an object
meters long= Time taken by the train to cover
meters
- Time taken by a train
meters long travelling at
km/hr to pass a man travelling at
km/hr in the same direction = Time taken by the train to cover a meters at
km/hr.
- Time taken by a train a meters long travelling at
km/hr to pass a man travelling at
km/hr in the opposite direction = Time taken by the train to cover a meters at
km/hr.
- Time taken by a faster train of length
meters travelling at
km/hr to over take a train of length b meters traveling at a speed of
km/hr in the same direction = Time taken by the train to cover
meters at
km/hr.
- Time taken by a faster train of length
meters travelling at
km/hr to over take a train of length b meters traveling at a speed of
km/hr in the opposite direction = Time taken by the train to cover
meters at
km/hr.
Problems on Boats and Streams
- If the speed of the boat is
m/s in still water and the speed of the stream is
m/s, then:
m/s
m/s
- If the speed of the boat down stream is
m/s and upstream is
m/s, then
m/s
m/s
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