Question

derivation of 3rd equation of motion

Answer 1

Distance=Average velocity * time
S=(v+u/2)*(v-u/a)
S=v square-u square/2a
2aS=v square-u square
v square=u square +2aS

((square means 2 written on top of the v and u))

Answer 2

Second equation of motion:

s = ut + 1/2 at^2

sol.

Let the distance travelled by the body be “s”.

We know that

Distance = Average velocity X Time

Also, Average velocity = (u+v)/2

.: Distance (t) = (u+v)/2 X t …….eq.(1)

Again we know that:

v = u + at

substituting this value of “v” in eq.(2), we get

s = (u+u+at)/2 x t

=>s = (2u+at)/2 X t

=>s = (2ut+at^2)/2

=>s = 2ut/2 + at^2/2

or s = ut +1/2 at^2

This is the 2nd equation of motion.