Official OCR A G481 mechanics 20th May 2013

Can anyone define the strength of a material, for example on a stress/strain graph or force/extension graph. What would show that the material is strong?

thanks for this, I better go learn how to tackle the 7 marker.

Yeah but i was doing some older papers where they didn't tell you the pivot where they gave you two forces and the weight and you had to determine where to take moments about to find one of the forces. So was curious as to whether we might have to do the same in these papers

If the material is strong then the graph would just have a straight line showing the material obeys Hooke's law and possible not showing it undergoing any plastic deformation, i doubt the graph would show its breaking point also if the question was to ask something about the strength...
If you were to work out the strength though (the stiffness) you'd work out the constant k, which would be the gradient in a f/x graph.

Yeah but i was doing some older papers where they didn't tell you the pivot where they gave you two forces and the weight and you had to determine where to take moments about to find one of the forces. So was curious as to whether we might have to do the same in these papers

Sometimes they tell you, sometimes they don't.. But if you take moments about a point that has an unknown force A acting on it you automatically eliminate A leaving you hopefully with only one unknown force, B

Ahh i see, so if there are 2 unknown forces and they ask you to determine one of the forces and you know the weight you take moments about the other force that has not been asked to find out?

Someone help me with january 2013 question 3c, confuses me.

Someone help me with january 2013 question 3c, confuses me.

The weight of the car acts directly down, so the horizontal component of the weight acts down the slope, so there is a larger force in the motion's direction (<---) Therefore as there is a greater force down the slope, the resultant force is increased, as mass is constant, the acceleration increases, increased acceleration means it has a higher velocity in the same time interval. Therefore it travels a greater distance.

Yeah but i was doing some older papers where they didn't tell you the pivot where they gave you two forces and the weight and you had to determine where to take moments about to find one of the forces. So was curious as to whether we might have to do the same in these papers

Ahh okay, so a strong material will have a really high ultimate tensile strength?

Yup because if K is big, then F is big (as f=kx), and so if F is big, the stress will be big as F/A=Stress, and a large value for stress means a high ultimate tensile strength

Can someone tell me the main points for trilateration? I get confused about whether signals are sent by the satellite or GPS

Ahh okay thanks a lot!



Radio/microwaves are sent from the SATELLITE, they are received by the GPS. The time taken for it to reach the GPS is determined, the speed of the waves are known ( speed of light, c, 3x10^8 ms^-1) so we can use time = distance/speed. To determine the distance that the car is away from the satellite. This is done by three or more satellites, as we know it is a particular distance from the satellite, but not exactly where it is from each satellite, we draw a circle, of radius of that distance. Drawing circles from each satellite, shows the possible places where the GPS/car is, where these circles intersect shows where the car MUST be. (This is the principle of trilateration.)

Can anyone go through how airbags/ seatbelts reduce impact on passengers?
This is what Ive got so far, Is there anything eles I need to say?
Seatbelts- prevents driver from moving through the windsheild due to its mass
Stretches a little which increases the distance the force can act it

Airbags: Works with seatbelts as it needs this time to inflate.
Sudden deceleration triggers reaction to inflate the bag.
Increases distance and time that force acts in.
reduces the deceleration on the driver.

THUS REDUCING THE AVERAGE FORCE IMPACTED ON PASSENGERS,

The weight of the car acts directly down, so the horizontal component of the weight acts down the slope, so there is a larger force in the motion's direction (<---) Therefore as there is a greater force down the slope, the resultant force is increased, as mass is constant, the acceleration increases, increased acceleration means it has a higher velocity in the same time interval. Therefore it travels a greater distance.