# (a) What do you understand by the kinetic energy of a body?(b) A body is thrown vertically upwards. Its velocity goes on decreasing. What happens to its kinetic energy as its velocity becomes zero?(c) A horse and a dog are running with the same speed. If the weight of the horse is ten times that of the dog, what is the ratio of their kinetic energies?

(a). Kinetic energy:  When an object is moving then the energy possessed by the object due to its motion is called its Kinetic energy. It is denoted by $K$ and SI unit of kinetic energy is $Joule$.

$\boxed{K=\frac{1}{2}mv^2}$

Here $m\rightarrow$ mass of the body or object

$v\rightarrow$ velocity of the body

(b).  When a body is thrown vertically upwards, its velocity goes on decreasing and finally it becomes zero at the maximum height. On the peak point, when its velocity becomes zero, then its kinetic energy also becomes zero and totally converted into gravitational potential energy.

(c). Here dog and the horse are running at the same speed let say it $v$.

Let $m$ be the mass of the dog then the mass of the horse will be $10m$.

So, kinetic energy of the dog $K_{dog}=\frac{1}{2}mv^2$

And kinetic energy of the horse $K_{horse}=\frac{1}{2}\times(10m)v^2$

So, $\frac{k_{dog}}{K_{horse}}=\frac{\frac{1}{2}mv^2}{\frac{1}{2}\times(10m)v^2}$

Or $\frac{k_{dog}}{K_{horse}}=\frac{1}{10}$

Or $K_{dog}:K_{horse}::1:10$

Therefore, the ratio of the kinetic energies of dog and horse is $1:10$.

Updated on: 10-Oct-2022

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