Define motion. What do you understand by the terms 'uniform motion' and 'non-uniform motion' ?Explain with examples. (a) Define speed. What is the SI unit of speed ? (b) What is meant by (i) average speed, and (ii) uniform speed.
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Solution
A body is said to be in motion when its position changes continuously with respect to a stationary object taken as a reference point.
UniformMotion: A body has uniform motion if it travels equal distances in equal intervals of time, no matter how small these time intervals may be. For example- a car running at a constant speed of 10m/s will cover equal distance of 10m every second, so its motion will be uniform.
Non−uniformmotion: A body has a non-uniform motion if it travels unequal distances in equal intervals of time. For example: dropping a ball from the roof of a tall building.
(a) The speed of a body is the distance travelled by it per unit time. The SI unit of speed is rn/s.
(b)
(i) The average speed of a body is the total distance travelled divided by the total time taken to cover this distance.
(ii) Uniform speed refers to the constant speed of a moving body. A body has a uniform speed if it travels the equal distance in equal intervals of time.