speed, distance and time

eddy2017

eddy2017

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Hi, dear teachers and friends. Hope you are all having a good day.
Mario and Luigi start at the spot. Luigi's car moves at a speed of 62mph and Mario's car drives at the speed of 47 mph in the opposite direction. If both drivers maintain a constant speed, about how many minutes will it take for them to be 77 miles away from each other?.

Thanks in advance for any help!,
eddy
 
Collecting data given
They both start at the same spot.
Luigi's car moves at 62mph.
Mario's car is going at 47mph but in the opposite direction.
both drivers will keep the same speed
how many minutes will it take for them to be 77 mile apart?
 
Let t be the time in hours.
How far does Luigi travel in t hours? What about Mario?
Then what should you do?
 
Thanks for the hint.
I'll apply this formula to Luigi. Let's see.
speed= distance traveled over time elapsed
62 mph= 77m/t
before I solve for t, am I right so far?
 
No, Luigi didn't travel 77 miles.
Answer my question. How far does Luigi travel? Your answer will be in terms of t.
 
eddy2017 said:
Collecting data given
They both start at the same spot.
Luigi's car moves at 62mph.
Mario's car is going at 47mph but in the opposite direction.
both drivers will keep the same speed
how many minutes will it take for them to be 77 mile apart?
Click to expand...
If you are sitting in Luigi's car with radar-gun, what would be Mario's speed that you would record?

Remember that Mario is moving in the opposite direction relative to Luigi!
 
No he doesn't. He travels at 62kmh mph for t hours. Recall that distance = speed x time.
 
Last edited by a moderator:
Oh, sorry. Mario is traveling 47 miles per hour.
Thanks!.
Mario's car is driving the opposite direction but he is 15 miles behind Luigi in relation to distance, right? . Is this a valid assumption?. Because it says that the speed is constant so they will keep this difference, i guess.
 
Last edited:
eddy2017 said:
Oh, sorry. Mario is traveling 47 miles per hour. Thanks!
Click to expand...
That is the "absolute speed of Mairo - measured by a "still observer".

What is the speed of Mario - relative to Luigi (who is travelling in the opposite direction)? - Think about it a little bit.....
 
Well, let me try this Hail Mary pass!:)
Do i sum up or substract the two speeds, so i can find the relative speed of Mario in relation to Luigi's?
 
eddy2017 said:
Well, let me try this Hail Mary pass!:)Do i sum up or substract the two speeds, so i can find the relative speed of Mario in relation to Luigi's?
Click to expand...
This should not be hail-Mary-pass. You should be able to think it out.

Suppose A and B are running side-by-side (along two parallel straight lines) in the same direction with the same speed. As time passes, would the distance between A and B keep on increasing or stay same or keep on decreasing?

When two points are moving (along two parallel straight lines) in the same direction the relative velocity (speed in this case) would be one subtracted from the other.

When two points are moving (along two parallel straight lines) in the opposite directions, the relative velocity (speed in this case) would be one added to the other.

Now...

What is the speed of Mario - relative to Luigi (who is travelling in the opposite direction)?
 
I will process all these explanations. I will write tomorrow. I just want you all to know that I am very grateful for the help and that I am classifying all the information I recieve from you. So it is not in vain.Thanks, you all have a good night. I will reply tomorrow morning.
 
eddy2017 said:
Hi, dear teachers and friends. Hope you are all having a good day.
Mario and Luigi start at the spot. Luigi's car moves at a speed of 62mph and Mario's car drives at the speed of 47 mph in the opposite direction. If both drivers maintain a constant speed, about how many minutes will it take for them to be 77 miles away from each other?.

Thanks in advance for any help!,
eddy
Click to expand...
Since Mario and Luigi is going in opposite directions (assuming straight and parallel stretch.

They are moving away from each other at a speed (47 + 62 = 109 mph = ) 109/60 miles/min

for a distance 109/60 mile they drive 1 minute

for a distance 1 mile they drive 60/109 minute

for a distance 77 miles they drive (60/109 * 77 =46220/19 = ) 42.385 = 42.4 minutes
 
Subhotosh has shown you one way to do the problem. Here's another way to get the same final answer.

Let t be the time in hours that Luigi and Mario travel.

Luigi travels at 62mph
Luigi's Distance = speed x time = 62 m/h x t hours = 62t miles
Mario travels at 47mph
Mario's Distance = speed x time = 47 m/h x t hours = 47t miles

If they are 77 miles apart then:

62t + 47t = 77
109t = 77
t = \(\displaystyle \frac{77}{109}\) hours
t = \(\displaystyle \frac{77}{109} * 60\) minutes
t ~ 42.4 minutes
 
Thanks a lot, Mr Subhotosh Khan and Mr Harry.
Just a couple of things to clear up.
The 60 minutes come from one hour?
Because they were going at...miles per hour. Is that the reasoning behind the 60 minutes?
Is that right?.
 
why t = 77 hours ?
109
why hours? if 77 is the amount of miles that they are going to be apart from each other?
why is there one unit rate there, hours? what is 109?.
 
eddy2017 said:
Thanks a lot, Mr Subhotosh Khan and Mr Harry.
Just a couple of things to clear up.
The 60 minutes come from one hour?
Because they were going at...miles per hour. Is that the reasoning behind the 60 minutes?
Is that right?.
Click to expand...
Mr Harry - That would be Ms. Harriett to you!!

eddy2017 said:
The 60 minutes come from one hour?
Because they were going at...miles per hour. Is that the reasoning behind the 60 minutes?
Is that right?.
Click to expand...
Those would be correct assumptions.
 
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