Which dog has the most kinetic energy?

a. a dog of mass 14 kg running with speed 2 m/s
b. a dog of mass 14 kg running with speed 3 m/s
c. a dog of mass 11 kg running with speed 5 m/s
d. a dog of mass 12 kg running with speed 4 m/s

Nobody actually needs to know how much kinetic energy any of these dogs has.  

The purpose of this question is to help you discover whether you know how to calculate kinetic energy, and then to give you some practice at doing it.

You have to calculate the kinetic energy of each dog, and then review your results to see which dog has the most.

The whole secret behind working this problem is the formula for the kinetic energy of any object:

Kinetic Energy = (1/2) · (mass) · (speed)²

The little ² next to 'speed' means 'squared' or 'multiplied by itself'.

(speed)² means (speed · speed) .

So, in order to calculate how much kinetic energy an object has, here's what you do:

-- Take the object's speed.  Multiply the speed by itself.

-- Take that number and multiply it by the object's mass.

-- Take that number and throw away half of it.

So now here we go:

Dog A:  KE = (1/2) (14 kg) (2 m/s)² = 28 Joules

Dog B:  KE = (1/2) (14 kg) (3 m/s)² = 63 Joules

Dog C:  KE = (1/2) (11 kg) (5 m/s)² = 137.5 Joules

Dog D:  KE = (1/2) 12 kg) (4 m/s)² = 96 Joules

==> Dog C has more kinetic energy than any of the other 3 dogs.

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