Question

a sphere of mass 2kg is thrown vertically downward from 8m height with velocity of 2m\s what is velocity of sphere at height of 5m?​

Answer 1

Let us take the point from which the sphere is thrown down as origin of the coordinate system, and the downward direction as positive.

The initial velocity of the sphere = +2 m/s, as it is directed downwards

Height from which the sphere is thrown = 8 m

Height at which the new velocity is to be found is 5 m ie after a downwards displacement (s) =+3 m

Using the formula:

v² - u² = 2 g s

Here,

u = initial velocity = +2 m/s (as it is directed downwards)

v = velocity acquired after a displacement of +3 m downward.

g = + 10 m/s², as the acceleration due to gravity is directed downwards

v² - 2² = 2 × 10 × 3 = 60, ==> v² = 4 +60 = 64;

v = ± 8 m/s, choosing the + sign as the velocity is directed downwards, we get velocity v = +8 m/s.

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Answer 2

Answer:

8 m/s.

Explanation: During free fall, the mass has no role to play.

Let the velocity at height of 5m. be v m/s.

Applying $v^{2}$-$u^{2}$=2as, we get,

$v^{2}$-4=2*10*3

$v^{2}$=64

v=8

Therefore the velocity at a height of 5m will be 8m/s.