# Homework Help: Help with kinetic and dynamic principles

1. Feb 24, 2010

### shibby_ftw

a train of mass 240 tonne is moving, at a speed of 84 km/h, up an incline of 1 in 90. the resistance to motion is 45 n per tonne. if power is removed, calculate the distance travelled along the incline before the train comes to rest

and

a railway wagon of mass 10 tonne travelling due east with a velocity of 14 kmh on a straight section of track collides with a second wagon of mass 12 tonne travelling due west at 3 km/h if thery are locked together after impact find the magnitude and direction of their common velocity.

i have no idea how to work it out, my notes have gone missing

i dont know where to begin, can someone help me with it please?
i dont mean do it for me i mean give me help in doing so, be it via email of instant message

2. Feb 24, 2010

### Lok

1. Are your notes really missing :P.

2. If you have the mass and speed of an object you can compute it's energy. If you know that it loses energy through climbing and friction (or whatever that is) in a constant manner than time is easy.

3. This is a plastic collision problem and energy will be lost (out of the system) whatever remains will decide your speed. Momentum is more useful in this problem.

3. Feb 25, 2010

### shibby_ftw

1. Are your notes really missing :P.

2. If you have the mass and speed of an object you can compute it's energy. If you know that it loses energy through climbing and friction (or whatever that is) in a constant manner than time is easy.

3. This is a plastic collision problem and energy will be lost (out of the system) whatever remains will decide your speed. Momentum is more useful in this problem.[/QUOTE]

haha yeahh they are actually missing, i dont know the forumla required to work it out, or how towork it out at all. im really bad at mechanical principles can you show me how to find out the forumla to use? are they based on the speed of the train and the friction?

and the resistance to motion is im guessed its 240 tonne so there is 45N per tonne slowing it down so theres 10800N acting on the train? how are newtons turned into speed? is it the same as gravity? so 9.81m/s ?and then times 10800? 105948 m/s divided by 1000 to make it km/h acting on the train so 105.948 km/h and its goes 84km/h so its slowing pretty fast? or am i well off?

4. Feb 25, 2010

### magwas

5. Feb 26, 2010

### shibby_ftw

6. Feb 26, 2010

### magwas

I guess it wants to mean that on 90 units of horizontal offset, there is one unit of horizontal offset.
so tg(alpha)=1/90

7. Feb 26, 2010

### Lok

U cannot turn everything into everything else. N are a measure of force, not speed. There are relations to energy spentthat will help. First find out what energy the train has at 84 km/h. expressed in joules.