Question

A small 20-kg canoe is floating downriver at a speed of 2 m/s. What is the canoe’s kinetic energy? 80 J 18 J 40 J 400 J

Answer 1

The answer is: 40 J.

To solve this problem you must apply the proccedure shown below:

1. You have the following formula that is used to calculate the kinetic energy:

$E_k=\frac{m*V^{2} }{2}$

Where m is the mass of the objetct and V is the speed.

2. Substitute values into the formula:

$m=20kg\\V=2m/s$

$E_k=\frac{(20kg)*(2m/s)^{2} }{2}$

3. Therefore, the result is:

$E_k=40J$

Answer 2

A Physics student on the river bank, watching the canoe float by, says that its kinetic energy is (1/2 m v²) = 40 Joules.

A Physics student in another canoe, floating alongside the first one, says that its kinetic energy is zero.

Both students are correct, each one for his own frame of reference.