ICSE Board: Suggested Books ICSE Board: Foundation Mathematics
Class 8: Reference Books Class 8: NTSE Preparation
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**Speed:** Speed of an object is 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 travelling with uniform speed. If not, it’s 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:
- Speed of the boat downstream m/s
- Speed of boat upstream m/s

- If the speed of the boat down stream is m/s and upstream is m/s, then
- Speed of the boat in still water m/s
- Speed of the stream m/s

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