Question

The kinetic energy of an object of mass, m moving with a velocity of 5 m s−1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?
Ncert Page :156

Answer 1

Given : K.E. of the object= 25 J
Velocity of the object, v= 5 m/s
∵ K.E.= 1/2 mv2
⇒ m= 2 x K.E./v2
⇒ m= 2 x 25 / 25 = 2 kg
If velocity is double, v= 2 x 5= 10 m/s
∴ K.E. (for v= 10 m/s)= 1/2 mv2 = 1/2 x 2 x 100= 100 J

If velocity is 3 times (tripped), v= 3 x 5= 15 m/s
∴ K.E. (for v= 10 m/s)= 1/2 mv2 1/2 x 2 x 225= 225 J

Answer 2

K.E. of the object= 25 J
Velocity of the object, v= 5 m/s
∵ K.E.= 1/2 mv2
⇒ m= 2 x K.E./v2
⇒ m= 2 x 25 / 25 = 2 kg
If velocity is double, v= 2 x 5= 10 m/s
∴ K.E. (for v= 10 m/s)= 1/2 mv2 = 1/2 x 2 x 100= 100 J

If velocity is tripled, v= 3 x 5= 15 m/s
∴ K.E. (for v= 10 m/s)= 1/2 mv2 1/2 x 2 x 225= 225 J