Not a Moment to lose, so stop Torquing!!

[Watson+Crick]

Hi there, I'm wondering if you guys can help me out? I'm currently looking at turning effect, moments and couples, and need some questions that are a little different to the basic:

 

"If the force is _____ distance from the pivot, what is the moment?" and "Use the principle of moments to show that the force is ____ N"

 

I'm currently studying AS physics, and would like something a little out of the box. Some criteria follow:

 

• The question naturally has to be hinged or pivoted
• It must follow the Theory of Moments
• Units are optional
• It must be entertaining

I have stopped using mock papers and the such because they are very limiting in the terms of entertainment issues -.-

 

Many thanks - I will answer the questions as they are posted, with working, correct or incorrect :/

Edited November 7, 2011 by Watson+Crick

[imatfaal]

Show with rough calculations why you should keep your chin tucked in when boxing

[Schrödinger's hat]

Here's some for you. Roughly in order of increasing difficulty. Depending on what level the course is/background you have, I wouldn't be surprised if you get stumped (possibly in part due to my poor wording).

 

 

 

Archimedes famously said: "Give me a place to stand and I shall move the earth."

Using torques, work out where you would have to stand to lift the Earth against the Sun's gravity (using an appropriate approximation for your strength) given that the fulcrum is 1 metre away from the contact point.

How much torque (from the fulcrum) is there on the lever?

 

(Yes, I know, it's moving; it's still a fun exercise even if it doesn't make sense. The force of gravity due to the sun at earth is [math]\frac{GM}{r^2}[/math] or an acceleration of g=0.006m/s^2, mass of earth is about m=6x10^24kg)

 

 

 

 

What advantage does having a patella give to a human? Show using a diagram and equations.

 

 

 

One way of measuring energy is force multiplied by (really integrated over, but not too important here) distance.

Power is energy divided by time.

With this in mind, what quantity in addition to torque would you need to measure to get the power of an engine?

 

 

 

 

 

 

Look up some figures about boat propellers (speed of rotation and horsepower of the engines).

Using what you worked out in the engine question, work out how strong the propeller shaft would need to be (how much torque it needs to withstand).

 

 

 

Model a motorcycle as a rectangular box of uniform density 1 m high and 1.8m long weighing 250kg including its rider.

Given that there is one force acting down on its centre of mass of mg, and a reaction force acting straight up at the 'rear wheel' (back of the rectangle) with equal magnitude:

What is the force (straight forward, from the same point -- back of the recangle -- as the upwards force) required to do a wheel stand?

 

Assume the bike is doing 80mph when this occurs, and that the engine is revving at 7000rpm.

What torque must the engine be producing?

(NB: this is an extremely simplistic model, so don't be surprised if the answer you get is at least a factor of two or so off)

 

Build a similar model for a car (maybe move the centre of mass further forward) and try to work out what power a car would need to produce to do a wheel stand.

 

 

 

Sail-boats Exhibit a phenomenon known as weather helm, wherein the tiller (stick on the rudder used to control it) will pull against the person steering the boat and cause a tendency to turn up-wind.

 

The opposite of this (called lee helm) is considered undesirable. An un-piloted boat pointing up-wind will come to a near-stop, whereas an un-piloted boat pointing down-wind will move at close to top speed.

 

Build a simple two dimensional (as in a childrens' drawing) model of a boat out of basic geometric shapes. Include a rudder and centreboard or keel.

 

Find the centre of resistance (directly analagous to centre of mass for constant density plane of uniform thickness) of the keel, rudder, and portion of the hull that is under water.

 

Find the centre of effort (same story) of the sails.

 

If these are not in the same place, what happens? What is the mechanism for this being exhibited as a torque on the rudder? What might you do to the position of the sails/keel to ensure that the boat does not develop lee helm -- whilst keeping the effect of weather helm small?

Edited November 8, 2011 by Schrödinger's hat