Question

4. A ball of mass 100 g is thrown upward. It rises to
a maximum height of 100 m. At what height its
kinetic energy will be reduced to 60%?
(1) 40 m
(2) 60 m
(3) 100 m
(4) 20 m
​

Answer 1

Answer:

answer is 60m option 2

Explanation:

mass of ball = 0.1g (1000g=1kg)

distance covered = 100m

initial velocity(u) is - 0= u2 - 2×10×100 (g=10m/s2)

so u2=2000m/s

kinetic energy initial is maximum = 1/2×0.1×2000=100J

60% of 100J = 60×100/100=60

kinetic energy when 60% reduces = 100-60=40J

v2 (velocity square) of ball when 40J is kinetic energy= 1/2×0.1×v2=40

so v2=800

so the conclution 800=2000-2×10×S(distance) according to equation v2=u2+2as

so distancie(S)= 60m

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