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Laws Of Motion

Question
CBSEENPH11016976

Derive an expression for centripetal acceleration experienced by a particle revolving in circular orbit of radius r with constant angular speed ω.

Solution
Let a particle revolve in a circular orbit of radius r with constant angular speed straight omega.
Let the particle starts from A and at any instant t, the particle be at B and undergo angular displacement θ = ωt. 
Linear speed of particle is v = rω.
Therefore the velocity of particle in vector form is, 
straight v with rightwards harpoon with barb upwards on top space equals space minus straight v space sin space ωt space straight i with hat on top space plus space rω space cos space straight j with hat on top

straight v with rightwards harpoon with barb upwards space on top equals space minus rω space sinωt space straight i with hat on top space plus space rω space cos space ωt space straight j with hat on top space

Now comma space differentiating space both space sides space straight w. straight r. to space straight t comma

fraction numerator straight d straight v with rightwards harpoon with barb upwards on top over denominator dt end fraction space equals space minus rω squared space cos space ωt space straight i with hat on top space minus space rω squared space sin space ωt space straight j with hat on top space

straight a with rightwards harpoon with barb upwards space on top space equals space left parenthesis negative rω squared space cos space ωt right parenthesis space straight i with hat on top space plus space left parenthesis negative rω squared space sin space ωt right parenthesis space straight j with hat on top space

The space magnitude space of space acceleration space is comma space

open vertical bar straight a with rightwards harpoon with barb upwards on top close vertical bar space equals space square root of space left parenthesis negative rω squared space cos space ωt right parenthesis squared plus space left parenthesis negative rω squared space sin space ωt right parenthesis end root space

space space space space space space equals space rω squared space equals space straight v squared over straight r space

The space angle space that space acceleration space makes space with space straight X minus axis space is comma space

tan space straight alpha space equals space fraction numerator negative rω squared space sin space ωt over denominator negative rω squared space cos space ωt end fraction space equals space fraction numerator negative space sin space ωt over denominator negative space cos space ωt end fraction

tan space straight alpha space equals space tan space left parenthesis straight pi space plus space ωt right parenthesis space

straight alpha space equals space straight pi space plus space ωt
Therefore, acceleration is directed along BO towards the centre. That is why it is known as centripetal acceleration.