OCR Physics A G481 Mechanics [Thursday 17th May 2012]

What do people reckon full ums boundary and A boundary will be

WHAT WAS THE ROCKETS ABOUT NET FORCE OR NET MOMENT? cause how can you assume that it creates a turning effect

My answers that i can remember

Acceleration was a vector quantity in the scalar section
Radius of satellite was 10m (2 sf)
For the slope question had mgsin(θ)=ma rearranging gets sinθ =a/g then a=2ms squared and g =9.8ms squared so θ=11.8 (3 sf)
magnitude of resultant force was 120N-90N (vertical component ) and horizontal component 18N, using Pythagoras got magnitude 35N (2 sf) and using inverse tan(30/18) got angle between resultant force and horizontal θ= 59.0
Velocity of horizontal component of projectile motion =24cos30
Velocity of vertical component of projectile motion =24sin30
Last question - Underwater turbines produce less noise pollution ? and absence of wind turbines makes environment aesthetically pleasing?
Satellite question - When both rockets are fired the satellite acts as a couple? there is rotation about a point but no linear acceleration ? and only when A is fired there is clockwise/anticlockwise motion not sure which way.
X is brittle where once the material exceeds its elastic limit it breaks. The material obeys hooke's law. The ultimate tensile strength of the material is where material breaks.
Y- Does not obey Hooke's law. When the force is removed the material returns to its original dimensions.

It was a glider and a spring. You had previously worked out the force. You are then given a time of 0.094 seconds (I think) and are told to work out the rate of work done.

Well there was a spring with force constant 50 and was compressed by 0.07 metres. The time the force was applied for - or something like that - was 0.094 seconds.
Really interested as to how everyone got 2.6 as i could not do this question for the life of me!

Wasn't the energy stored in the spring 1/2kx^2
So the energy stored was 0.5 x 50 x 0.07^2 = 0.1225 j
So energy done per second is 0.1225 / 0.094 = 1.30

I left my answer as 1.30 so I must of missed something... but oh well.

I got 2.6 but just realised its 1.3

I did work done/time

So I did the force x distance / time

However work done for a spring is area under a graph

So its half the force times distance / time which is 1.3

Bugger

I think everyone did as everyone thinks 2.6 is the right answer...

why is it not 1/2 kx^2

I got all the same answers and you did. Apart from the last question. I put something different which I think was wrong :/ But still happy

to be honest i don't know , i believe the 1/2 only applies for areas under an force/extension (or length) graph.

The reason i put 2.6W was because i used the other way to work out power. Where mass x acceleration x distance (extension) divided by time gave the same answer.

GG

The work which a spring does is 1/2Fx or 1/2kx^2, as thats its elastic potential energy; anyway what do you reckon full ums boundary will be

Yeah i think your right about 1/2kx(squared) so it must be 1.3W. i thought the A grade will be slightly lower 45/60 as it seemed alot harder compared to other past papers :/ but its only my opinion

for the further reason why it is better for last question i said about energy supply is constant

What did you guys get for the radius? 10?

Cannot believe car safety or GPS did not come up... unbelievable

i thought it was because there was no movement in the vertical direction?

not sure :/, but because that turbine was in the water, so water will always be available to make electrical power, and a wind turbine relies on there being wind, if no wind, no energy can be produced