Video Transcript
A hummingbird has a mass of 40 grams. The hummingbird flies in a straight line between two flowers 18 meters apart in a time of 12 seconds. What is the average kinetic energy of the hummingbird while flying between the flowers?
Let’s begin by drawing a diagram. Here is the hummingbird while it’s flying a distance of 18 meters between the two flowers. We can call this distance Δ𝑑 because it’s the hummingbird’s change in displacement over a change in time Δ𝑡 of 12 seconds. We also know that the hummingbird has a mass 𝑚 of 40 grams. We want to know its average kinetic energy while it’s flying between the flowers.
So, recall that we can calculate the kinetic energy of an object using the formula one-half 𝑚𝑣 squared, where 𝑚 is its mass and 𝑣 is its velocity. We already know the mass of the hummingbird, but we don’t know its velocity. So we’ll need to calculate it. We can find the hummingbird’s average velocity using the formula distance divided by time. We already know values for both of these terms expressed in base SI units. So, substituting in Δ𝑑 and Δ𝑡, we have 18 meters divided by 12 seconds, which equals 1.5 meters per second.
Alright, now that we know the hummingbird’s mass and average velocity, we’re ready to calculate its average kinetic energy. We have one-half times mass times velocity squared. But notice that mass is currently written in grams. So we should convert it to kilograms in order for our answer to come out in base SI units. Remember, the SI unit of energy is the joule, which is equivalent to a kilogram meter squared per second squared. We can recall that a kilogram is equal to 1000 grams. So, to convert, we should move the decimal point of the gram value one, two, three places to the left.
Now, applying this to our mass value in the formula, we now have one-half times 0.040 kilograms times 1.5 meters per second squared, which comes out to exactly 0.045 joules. And thus we have our answer. While flying between the flowers, the hummingbird has an average kinetic energy of 0.045 joules.
