Question

The ball has a mass 1kg resting at a height 10m from ground find its potential energy, kinetic energy and velocity of ball? (b) Find potential energy, kinetic energy and velocity of ball when it is half the way to reach ground?

Answer 1

a.)

Initial potential energy given by,

PEi = m*g*h

here, m = mass of ball = 1 kg

g = 9.81 m/s^2

h = height of ball = 10 m

then, PEi = 1*9.81*10

PEi = 98.1 J

Initial kinetic energy will be:

KEi = 0.5*m*vi^2

here, vi = initial speed of ball = 0 (As it is in rest.)

then, KEi = 0.5*1*0^2

KEi = 0

b.)

now, hf = final height of ball = h/2 = 5 m

then, final potential energy of ball = PEf = 1*9.81*5

PEf = 49.05 J

using energy conservation,

PEi + KEi = PEf + KEf

then, final kinetic energy(KEf) = 98.1 + 0 - 49.05

KEf = 49.05 J

now, KEf = 0.5*m*vf^2

then, vf = final speed of ball = sqrt(2*KEf/m)

vf = sqrt(2*49.05/1)

vf = 9.9 m/sec.

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