Q. 7
Write true or false for the following statements :
When velocity is halved, its kinetic energy becomes 1/4th.
Answer :
True
Explanation: Kinetic energy KE of a body of mass m moving with velocity or speed v is given by the formula:
KE = 
m v2
so kinetic energy is directly proportional to the mass of object and to the square of speed of the body.
KE1 = 
mv12
If the velocity of body is halved then kinetic energy
KE2 = 
mv22 where, v2 =
v1
Substituting the value of v2 in the formula,
KE2 = 
m (
v1)2
= 
(
mv12)
KE2 = 
KE1
So kinetic energy will become 1/4 if the speed is halved.
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