Physics question. Now I know why I didn't want to stay long in school.

[Timma]

Ok so I have a question and i'm stumped. Going back to school to get another degree and I have to take physics AGAIN.

A bicyclist is finishing his repair of a flat tire when a friend rides by at 3.5 m/s. Two seconds later, the bicyclist hops on his bike and accelerates at 2.4 m/s squared until he catches his friend. a.) How much time does it take till he catches his friend? b.) How far has he traveled in this time? c.) What is his speed when he catches up?

This is what happens when you've been out of school for over three years. I feel like a complete retard cause I was always good at this stuff.

[Scrumhalf]

Easy. The key to remember is that the distance both of them cover is the same.

Assume the time it takes the cyclist to catch up to his friend is t.

Distance covered by friend = 3.5 x (t+2) = 3.5t + 7
Distance covered by cyclist = 0.5 x 2.4 x t^2 = 1.2 t^2

(I use the symbol ^2 to refer to the square)

Since the distance covered by both is the same,

1.2 t^2 = 3.5t + 7

Solving this quadratic equation, you get t = 4.28 sec

a) It takes 4.28 sec for the cyclist to catch up to his friend

b) distance traveled = 3.5 x (4.28 + 2) = 21.98m

c) speed of bicyclist when he catches up to his friend = acceleration x time
= 2.4 x 4.28 = 10.27 m/sec

[Timma]

:bravonew: Thanks man I appreciate the help. See it's amazing what you forget when you don't use it every day.

[Scrumhalf]

No problem.... I like doing these.... dusts off the cobwebs in the darkest recesses of my brain. Gotta solve some differential equations and do integration by parts one of these days - I used to be a whiz at these but haven't done one in about 12 years since I got out of grad school lol....

[rado]

Originally Posted by Scrumhalf

Easy. The key to remember is that the distance both of them cover is the same.

Assume the time it takes the cyclist to catch up to his friend is t.

Distance covered by friend = 3.5 x (t+2) = 3.5t + 7
Distance covered by cyclist = 0.5 x 2.4 x t^2 = 1.2 t^2

(I use the symbol ^2 to refer to the square)

Since the distance covered by both is the same,

1.2 t^2 = 3.5t + 7

Solving this quadratic equation, you get t = 4.28 sec

a) It takes 4.28 sec for the cyclist to catch up to his friend

b) distance traveled = 3.5 x (4.28 + 2) = 21.98m

c) speed of bicyclist when he catches up to his friend = acceleration x time
= 2.4 x 4.28 = 10.27 m/sec

WTF....I was always good with physics, but damn I've forgot so much of this shit.

[BBAddict]

Originally Posted by Scrumhalf

No problem.... I like doing these.... dusts off the cobwebs in the darkest recesses of my brain. Gotta solve some differential equations and do integration by parts one of these days - I used to be a whiz at these but haven't done one in about 12 years since I got out of grad school lol....

I just found myself doing diff eq's last week for a work project--that took me back a ways! Good to force yourself to do once in a while, but not too often. What did you go to grad school for--some kind of engineering?

[Puddles]

He would have accellerated much faster if his friend was this girl...

[Severedties]

ahaha.. Good one puddles

[Scrumhalf]

Originally Posted by BBAddict

I just found myself doing diff eq's last week for a work project--that took me back a ways! Good to force yourself to do once in a while, but not too often. What did you go to grad school for--some kind of engineering?

Ph.D in Electrical Engineering. Graduated in 1990 though, so it's been a while!

[Timma]

Originally Posted by Scrumhalf

Ph.D in Electrical Engineering. Graduated in 1990 though, so it's been a while!

That's awesome bro. I have twin cousins that got theirs a few years back as well. The shit I saw them do to get it was incredible.

[Timma]

Originally Posted by Puddles

He would have accellerated much faster if his friend was this girl...

Hell I would have kept riding with the damn flat tire.

[BBAddict]

Originally Posted by Scrumhalf

Ph.D in Electrical Engineering. Graduated in 1990 though, so it's been a while!

Materials Engineering for me. When I graduated (~2000), I wished I had an EE with Computer Science cause those guys were getting rediculous offers straight out of school.