Question

A puppy weighing 3 kilograms races through the dog park. If she slows from a speed of 2 meters/second to 1 meter/second, what will happen to her kinetic energy?

Answer 1

Answer: Kinetic energy will be decreases by 4.5 Joules.

Step-by-step explanation:

Kinetic energy is the energy which is possessed by the virtue of objects motion. It is defined as the product of object's mass and square of the objects's velocity.

Mathematically,

`K=(1)/(2)mv^2`

Change in kinetic energy will be:
`K=\frac{1}[2}m\Delta v^2`

where,

m = mass of the object = 3 kg

`\Delta v=v_2-v_1` = Change in velocity

`v_1=2m/s\\v=1m/s`

Now, calculating the change in kinetic energy:

`K.E.=(1)/(2)* 3kg* (1^2-2^2)m^2/s^2=-4.5J`

Negative sign indicates that the kinetic energy is getting reduced.

Hence, kinetic energy will be decreases by 4.5 Joules.

Answer 2

Ans: Thus, the kinetic energy change = 4.5 J

The mass of puppy = 3kg

Kinetic energy initial =
`(1)/(2) mv^(2)`
=
`(1)/(2)*3*4 = 6 kg-m/s2`

Kinetic energy final =
`(1)/(2) mv^(2) = (1)/(2)*3*1 = 1.5 kg-m/s2`

Thus, the kinetic energy change = 4.5 J