**Question 2:** Define the following:

Speed | Uniform speed | Variable speed | Instantaneous speed | Average speed |

**ANSWER**

**Speed:** Distance covered by a body in one second is called its speed.

If a body travels distance ‘s’ meters in time ‘t’ seconds, then its speed ‘v’ is given by the equation,

While talking of speed, the direction of motion is not taken into account; speed being a scalar quantity.

Its unit is m/s and dimensions are [LT^{-1}].

**Uniform Speed:** If a body covers equal distances in equal intervals of time, its speed is said to be uniform.

**Variable Speed:** Let the 20 seconds journey is divided into four equal intervals of 5 seconds each. If the distances covered in these intervals are unequal, for example, 2 m, 4 m, 6 m and 7 m, the speed of the body is said to be variable. Therefore, the speed of a body is said to be variable if the body covers unequal distances in equal intervals of time. (Apply this example to the uniform speed above).

**Instantaneous Speed:** Let the speed of a body is continuously changing during the course of its journey. Instantaneous speed is then defined as *the speed of the body at a particular interval of time.* As the speed is continuously changing, this particular instant must very small. If the small interval is denoted by ∆t and the small distance it covers during this time is ∆s, then the mathematical form of the instantaneous speed is

The essence of this equation is that ∆t is very very small.

**Average Speed:** Average speed is obtained by dividing the total distance covered by total time.

If ‘S’ meters are covered in‘t’ seconds, then

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