Physics hw question need help?

Question

The Olympic record for the marathon is 2 hours 9 mins 21 seconds. The marathon distance is 26 miles 385 yards. Determine the average speed (in miles per hour) of the record.

Answer 1

1 minute = 60 seconds

1 hour = 60 minutes

You have to convert time into hours.

9 mins * (1 hours/60mins) = x hours.

21 seconds * (1 min/60seconds) * (1 hour/60 minutes) = y hours.

Add 2 hours + x + y to get the time in hours.

Now convert the distance into miles.

1 yard = 12 feet.

1 mile = ? feet.  Find a table for this. I'm guessing but I think its 5280 feet.

385 yards * (12 feet/yard)  * (1 mile/5280 ft) = z miles.

Add 26 + z to find the distance in miles.

speed = distance/time.  Also you should write the division using a horizontal line instead of a slash symbol.

Answer 2

There are 1760 yards in a mile, so 385 yards is 385/1760 = .21875 miles.  Therefore, the marathon distance is 26.21875 miles.  2 hours, 9 minutes and 21 seconds is 2 + 9/60 + 21/3600 = 2.1558333... hours.  We need to do that to get everything in consistent units.  Therefore, since average speed is path length over time,

v = 26.21875 miles/2.1558333... hours ~ 9.84248 miles per hour

I'm going to let you worry about significant digits.