Question

A girl and her dog are running. The dog has a mass of 20kg. The girl has a mass of 60 kg. Suppose both the dog and the girl run at a speed of 2 m/sec. Calculate both of their kinetic energies. Show your work.
Suppose the dog speeds up and is now running at a speed of 4 m/sec. Calculate the dog's kinetic energy. Show your work.

Answer 1

Answer:

1i) Girl's K.E = 120 J

1ii) Dog's K.E = 40 J

2) Dog's K.E = 160 J

Explanation:

1) K.E = $\frac{1}{2} mv^{2}$

i) where the Girl has mass 60 kg and speed 2 m/s

Girl's K.E = $\frac{1}{2} X 60 X 2^{2}$

K.E = 0.5 X 60 X 4 = 120 J

ii) where the Dog has mass 20 kg and speed 2 m/s

Dog's K.E = $\frac{1}{2} X 20 X 2^{2}$

K.E = 0.5 X 20 X 4 = 40 J

2) where the Dog has mass 20 kg and speed 4 m/s

Dog's K.E = $\frac{1}{2} X 20 X 4^{2}$

K.E = 0.5 X 20 X 16 = 160 J

Answer 2

Using $K = \frac{1}{2}mv^2$, we can say that the girl's kinetic energy is 120 and the dog's is 40. If the dog speeds up, it now has a kinetic energy of 160.