# Which trolley would turn in the smallest circle?

1. Aug 27, 2011

### Dcoz

Hi, my first post here is a simple one (hopefully) and is a from a series of mechanical comprehension questions I had been given.

I have no idea which one is correct. If you do know the answer would you be able to give a brief explaination to why it is?

Also, if anyone has any mechanical comprehension resources (such as test sheets with answers) I would be very grateful.

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2. Aug 27, 2011

### lewando

You really should try to imagine which one would have the best/worst turning radius. It's a good exercise. Since you are new to PF and have successfully figured out how to attach the attachment, here's a clue: think about the steering dynamics of a very long fire engine and the job of the person behind the steering wheel in the back of the vehicle.

As a suggestion for getting a better physical understanding of mechanical concepts, you can start by building three models of the cars in the problem and observing firsthand how they work. Shouldn't take too long to do.

3. Aug 27, 2011

### Dcoz

Thank you for your hint. I actually wanted to build these models to help prove it, but unfortunately having an open book exam on the 2nd, time is currently against me and now am just trying to continue to build my notes through examples.

It could just be a mental block, but sadly your hint means very little to me other than that the driver may potentially have to turn later to prevent the rear of the vehicle from going over the inside of the turn.

4. Aug 27, 2011

### lewando

That is exactly the job of the rear driver! Without the rear driver, the turning radius would be huge and impossibly huge for navigating 90 degree turns on city streets. Three questions for you:
1. What direction must the driver orient the rear wheels (say with respect to the body of the vehicle) to do this correctly?
2. Knowing this, how does the direction of the rear wheels compare to the direction of the front wheels, during a turn.
3. Which model as the best chance of achieving this same front/rear directional mode? (hint: you should be able to rule one of them out, by now)

5. Aug 27, 2011

### Dcoz

I never knew some fire trucks had two drivers, well at least I've never seen it here in the UK.

1. Not sure how to answer this directly, but I'm assuming questioning 2. will solve it.
2. They turn in opposite directions.
3. B.

6. Aug 27, 2011

### lewando

Very good. Here is a relevant video to drive home the point:

Good luck with exams!

Last edited by a moderator: Sep 25, 2014
7. Aug 27, 2011

### Dcoz

Thank you that video did really help! Just can't believe I couldn't answer that question after playing Halo.

Anyway thanks again!

Oh by the way did you have any resources along with the their solutions.

8. Aug 27, 2011

### lewando

Not really. You should explore this site's learning materials, maybe some good references.
https://www.physicsforums.com/forumdisplay.php?f=181
I have used Schaum's Outlines and would recommend them if your textbook is not extensive enough for you.
http://www.mhprofessional.com/category/?cat=3959 [Broken]

Last edited by a moderator: May 5, 2017