The Magic Café
Username:
Password:
[ Lost Password ]
  [ Forgot Username ]
The Magic Cafe Forum Index » » Puzzle me this... » » The running dog (0 Likes) Printer Friendly Version

Top Hat
View Profile
Inner circle
We peed on you!
1077 Posts

Profile of Top Hat
A marching troop - that is, rows of soldiers walking forward in a straight line - is 25 metres long (from the first soldier at the front to the last soldier at the back). It is marching at a constant speed of 1 metre per second.

The regimental dog (located at the heel of the last soldier) runs forward from the last soldier to the first soldier. When it reaches the first soldier it turns round and runs back to the last soldier. By the time it finishes this run, the troop has moved forward by exactly 25 metres.

Assuming no acceleration or deceleration of the dog, what is the dog's speed?
TH Smile Smile Smile Smile Smile
magicgeorge
View Profile
Inner circle
Belfast
4299 Posts

Profile of magicgeorge
Time is 25 seconds
Let speed of dog =x
Dogspeed relative to line is x-1 on the way up and x+1 on the way back

therefore
25=25/x-1 + 25/x+1
(x-1)(x+1)=(x-1)+(x+1)
0=x^2 -2x -1
Quadratic. I get this:
Dog speed=2.4142135 mps
The Magic Cafe Forum Index » » Puzzle me this... » » The running dog (0 Likes)
[ Top of Page ]
All content & postings Copyright © 2001-2019 Steve Brooks. All Rights Reserved.
This page was created in 0.19 seconds requiring 5 database queries.
The views and comments expressed on The Magic Café
are not necessarily those of The Magic Café, Steve Brooks, or Steve Brooks Magic.
> Privacy Statement <

ROTFL Billions and billions served! ROTFL