Jump to content
student_lfcs

Motion - To find force

Recommended Posts

Ques: An 8000 kg engine pulls the train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 newton and the track offers a frictional force of 5000 newtons then calculate the force of wagon 1 on wagon 2.

 

Ans ( I tried) : Total weight =18,000 kg

Net force exerted= 40000 - 5000 = 35000

Accelration: 35000 / 18000 = 35 / 18 = 3.5 m/s^2

Share this post


Link to post
Share on other sites
Quote

Ans ( I tried) : Total weight =18,000 kg

kg are a measure of mass not weight.

 

12 minutes ago, student_lfcs said:

Net force exerted= 40000 - 5000 = 35000

Is the net force the same between all parts of the train?

 

Share this post


Link to post
Share on other sites

Ok. Please see if I am right this time:

Total mass =18,000 kg

Net force exerted= 40000 - 5000 = 35000

Accelration: 35000 / 18000 = 35 / 18 = 1.95 m/s^2

force exerted by wagon 1 on wagon 2: Accelration x Mass

Mass in this case = 4 x 2000 = 8000 kg; Accelration is same i.e. 1.95 m/s^2

So F = 8000 x 1.95 = 15555 N

Share this post


Link to post
Share on other sites
Posted (edited)
1 hour ago, student_lfcs said:

Ok. Please see if I am right this time:

Total mass =18,000 kg

Net force exerted= 40000 - 5000 = 35000

Accelration: 35000 / 18000 = 35 / 18 = 1.95 m/s^2

force exerted by wagon 1 on wagon 2: Accelration x Mass

Mass in this case = 4 x 2000 = 8000 kg; Accelration is same i.e. 1.95 m/s^2

So F = 8000 x 1.95 = 15555 N

OK that looks a whole lot better.

:-)

Hopefully you feel good too since I didn't do it for you, just offered a hint.

 

One small niggle.

My calculator says that 35/18 = 1.94 not 1.95.

In fact there is no need to work this out at all.

Just leave the common acceleration* as


[math]\left( {\frac{{35}}{{18}}} \right)[/math]


Then you can multiply it all out at the end.

Very often something will cancel out and make it even easier.


[math]F = ma = 8000*\left( {\frac{{35}}{{18}}} \right)[/math]

 

 * Notice also how to spell acceleration.

Edited by studiot

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.