Go Back   Physics Help Forum > High School and Pre-University Physics Help > Kinematics and Dynamics

Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old Sep 23rd 2010, 10:39 PM   #1
Junior Member
 
Join Date: Sep 2010
Posts: 2
Arrow Kinematics

A train is moving parallel and adjacent to a highway with a constant speed of 21 m
/s. Initially a car is 60 m behind the train, traveling
in the same direction as the train at 35 m
/s and accelerating at 3 m/s^2.
What is the speed of the car just as it passes the train?
Answer in units of m
/s.

I have a basic understanding of the problem. I'm trying to find out what Vf of car is when Vf of the car > Vf of the train. But, I'm confused. Is it saying that the Vi of the train is 35 m/s?? Or is the Vi of the train = 0 (Because we have to assume that a train has to stop at one point before it starts again.)

I wish I could put my diagram i drew here, but i can't.

hah842 is offline   Reply With Quote
Old Sep 24th 2010, 06:09 AM   #2
Member
 
Join Date: Jul 2009
Posts: 72
the train doesnt stop

the car passes the train because its faster

you need to write the equations of motion of the car and the train
Haytham is offline   Reply With Quote
Old Sep 24th 2010, 08:31 AM   #3
Physics Team
 
ChipB's Avatar
 
Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,347
The velocity of the train is constant at 21 m/s. So it's position as a function of time is x_train = x_0 + vt = 60 m + 21m/s x t

The car is accelerating, so it's position is determined by:

x_car = v_i x t + 1/2 at^2 = 35m/s x t + 1/2 x 3 m/s^2 x t^2

Set these two equations equal, and solve for t. IYou can then put that value for t into an equation for the velocity of the car:

v_car = v_i + at
ChipB is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Kinematics and Dynamics

Tags
kinematics, physics, two dimensional motion, velocity



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Kinematics help!? nolanbradshaw01 Kinematics and Dynamics 1 Nov 20th 2015 04:38 AM
Kinematics amit6234623 Kinematics and Dynamics 1 Oct 8th 2015 06:13 AM
Kinematics Aladdin Kinematics and Dynamics 8 Apr 3rd 2011 11:08 AM
Kinematics Help Fazil Kinematics and Dynamics 5 Mar 20th 2009 11:47 AM
kinematics, please help, devanlevin Kinematics and Dynamics 0 Nov 17th 2008 09:25 AM


Facebook Twitter Google+ RSS Feed