Question

A small 22 kilogram canoe is floating downriver at a speed of 3 m/s. What is the canoe's kinetic energy?

Answer 1

Kinetic energy = 1/2 (mass)(speed squared).

According to somebody on the river bank watching the canoe float by, it has 99 joules of kinetic energy.

According to anybody in another boat, floating down the same river, the canoe has no kinetic energy at all.

They're both correct, each in his own frame of reference.

Answer 2

Kinetic energy can be calculated using the following rule:
kinetic energy = 0.5*m*v^2 where:
m is the mass = 22 kg
v is the velocity = 3 m/sec

Substitute with the givens in the above equation to get the kinetic energy as follows:
kinetic energy = 0.5(22)(3)^2
kinetic energy = 99 Joules