Physicsbodies in motion word problem

flnursegirl

New member
A plane makes a trip of 246 miles. For some amount of time the planes speed is 115 mph. For the remainder of the trip the planes speed is 250 mph. If the total trip time is 72 minutes, how many minutes did the plane fly at 115 mph?

Klaas van Aarsen

MHB Seeker
Staff member
A plane makes a trip of 246 miles. For some amount of time the planes speed is 115 mph. For the remainder of the trip the planes speed is 250 mph. If the total trip time is 72 minutes, how many minutes did the plane fly at 115 mph?
Hi flnursegirl! Welcome to MHB!

Let's call $x$ the number of minutes that the plane flew at 115 mph, which is what we want to know.
Then the distance the plane traveled in those $x$ minutes is:
$$\frac{x \text{ minutes}}{60\text{ minutes/hour}} \cdot 115 \frac{\text{mile}}{\text{hour}}$$
The distance the plane traveled in the remaining time is:
$$\frac{(72- x) \text{ minutes}}{60\text{ minutes/hour}} \cdot 250 \frac{\text{mile}}{\text{hour}}$$

So the total distance is:
$$\frac{x}{60}\cdot 115 + \frac{72-x}{60}\cdot 250 = 246 \text{ miles}$$

Can you solve that equation?

flnursegirl

New member
No can you show me more?

topsquark

Well-known member
MHB Math Helper
No can you show me more?
Please be specific. What more help do you need? The derivation or solving the equation?

-Dan

flnursegirl

New member
Need help to solve the word problem

Klaas van Aarsen

MHB Seeker
Staff member
Need help to solve the word problem
Erm... I've converted the word problem into an equation...
That sort of solves the word problem doesn't it?
Do you need more help to solve the equation, or to understand how the word problem was converted into an equation?
What do you need help with exactly?

flnursegirl

New member
Could you show how to solve the equation?

Klaas van Aarsen

MHB Seeker
Staff member
Could you show how to solve the equation?
So the total distance is:
$$\frac{x}{60}\cdot 115 + \frac{72-x}{60}\cdot 250 = 246 \text{ miles}$$
Okay... it's like:

$$\frac{x}{60}\cdot 115 + \frac{72-x}{60}\cdot 250 = 246 \text{ miles} \\ \Rightarrow x \cdot \frac{115}{60} + \frac{72}{60}\cdot 250 - x \cdot \frac{250}{60} = 246 \\ \Rightarrow x\left(\frac{115}{60} - \frac{250}{60}\right) = 246 - \frac{72}{60}\cdot 250 \\ \Rightarrow x = \frac{246 - \frac{72}{60}\cdot 250}{\frac{115}{60} - \frac{250}{60}} = \frac{246\cdot 60 - 72\cdot 250}{115 - 250} = 24 \text{ minutes}$$

flnursegirl

New member
Thanks! I got it!