Physics question about distance traveled and average speed please help explain
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Physics question about distance traveled and average speed please help explain

[From: ] [author: ] [Date: 11-08-29] [Hit: ]
so average speed is distance / time = 203 * 3/10 = 60.(a)Distance from home to school is 155.(b)Average speed is 46.7 miles per hour.This is pretty straightforward.But it looks mean.......
You are driving home from school steadily at 65 mph for 130 miles. It then begins to rain and you slow to 55 mph. You arrive home after driving 3 hours and 20 minutes. (a) How far is your hometown from school? (b) What was your average speed? --- I know that you need distance traveled in order to find part b ( average speed) but how do you find distance traveled?

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You need to find the TIME for each segment.
In the first section 65 mph for 130 miles
we have v = s/t or t = s/v = 130 / 65 = 2 hrs

Therefore he went at 55 mph for 1hr and 20 minutes ( = 4/3 hrs)
In this time he moved 55 * 4/3 = 73 miles

so the total distance travelled was 130 + 73 = 203 miles

and the total time was given as 3hr 20 = 10/3 hrs

so average speed is distance / time = 203 * 3/10 = 60.9 mph

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Answers -->

(a) Distance from home to school is 155.8 miles
(b) Average speed is 46.7 miles per hour.

This is pretty straightforward. But it looks mean. It's not.

r1 = 65 miles per hour
d1 = 130 miles

So right away, you have at least 130 miles to school. Since Distance = Rate * Time, you can calculate how long it took you to drive those 130 miles, solving for time

D = R / T

T * D = R

T = R / D

T1 = (65 mi/hr) / (130 mi)

T1 = 0.5 hours (30 minutes; units of miles canceled)

You're given the total time

TT = 3 hr, 20 min

Put that in terms of minutes

(3 hr) * (60 min / 1 hr) = 180 minutes + 20 minutes = 200 minutes

You know you were driving the first leg only took 30 minutes, so the remaining leg took

T2 = (200 min) - (30 min)

T2 = 170 min

Now you have time and speed for the second leg, you can solve for distance (put hours in terms of minutes for the equation)

D = (55 mi/hr) * ( hr / 60 min) * ( 170 min) <--- ( 1 hr / 60 min) converted to minutes

Distance from home to school = 155.8 miles

Now on to the second part.

You know total time (200 minutes) and you know total distance (155.8 miles), just solve for total average speed, using a conversion back to hours (60 min/hr)

R = (155.8 mi) / (200 min)

R = (0.779 miles/min) * (60 min/hr)

R = 46.7 miles per hour.

And your'e done!

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distance is 130 + 55*80/60=203.3333miles
speed =203.333333/(200/60) =61 miles/hour

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t = S1/V1 = 130/65 = 2 hrs. So S = S1 + V2(T - t) = 130 + 55*(3.3 - 2) = 201.5 miles to the house. a)

Vavg = 201.5/3.2 = 63.0 mph b)
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