*MEGATHREAD* - The 2014 entry BMAT Thread - Page 70

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thanks so much! literally wish I could trade my brain with some of the people on this. could I bother you with three more questions which are confusing me? (one of them is on circuits which you would like - the answer is E and I'm just confused why V1 is smaller than V2 :s
the answer to the pulley question is 2m/s2 and the box plot is E pulley 2006.jpg

thanks so so much!

Q16: You need to use the equation F=ma. You know mass butyou need to find the resultant force before finding out the acceleration
So resultant force is upward forces -downward force
Upward force= 120+120=240N
Downward force(weight)=mg=20*10=200N
Resultant=240-200=40N
F=ma
a=F/m=40/20=2ms-^2

Q20: All 5 resistors have same resistance as they are identical. Lets suppose each resistor has value of 10ohms.
And suppose the total V=20volts

Now you know that the voltage in parallel is same across each line. So 2 resistors are in top line( consider this as one resistance) and 3 are in bottom line( consider this as another resistance). The Voltage should divide equally between these 2 parallel combinations so upper part should get 10V and lower should get 10V. Now the upper two are connected in series with each other so 10V will split between 2 and each will have 5V.

Coming to the lower part, here there is another parallel combination. As the equivalent resistance of the R3 and other lets say R5 is 5ohms it will get voltage less than 5volts. Lets say It will only get 2.5V. The remainig for bottom part is 10-2.5=7.5V that will go through R2.
Anpther point to make clear that voltage always split in proportion to the resistance value. The one with higher resistance wil have higher voltage. As parallel combination (R3,R5) have low total resistance i.e 5ohms so they will have lower share of voltage and R2 has 10ohm resistance so it will have a higher share i.e 7.5V.
So V2>V1>V3
I know its a really long explanation but it would be better if u had done AS Physics.

Q8: I have never done probability topic in my school and college as i have come from a different country so i always guess these questions :biggrin:

Fell free to ask me if u don't understand :smile:

(edited 10 years ago)

Reply 1381

dwindledStrangly

Original post by Ambitions

I just guess for those type of questions (to lazy to read!). I use any spare time left at the end of the paper to check over other answers. But perhaps it would be wiser to attempt them properly haha...

Lol, i was thinking to do that but i noticed they come up 2 - 3 times a paper so that's immediately 12 questions wrong (i assume guessing gets now marks, but hope it gets them all).

Reply 1382

dwindledStrangly

Original post by Edison'sWords

read the questions and answers first, that way you know what they're looking for and plus, some questions refer to a paragraph so you don't need the whole text to find that answer :smile:

Thanks, i'll try that.

Reply 1383

Herisson

Original post by pinkdiamond1001

thanks so so much!

Boxplot:
By definition a quartile has a quarter of the whole sample, so any random person in the sample has 1/4 chance of being in that quartile. Chance of all three is (1/4)^3=1/64

Reply 1384

prafto

Original post by BeckiFlute(:

Not just you! I'd been getting scores of 8+ until that one!

8+?!?! woah! Any tips? :biggrin:

Reply 1385

holly432

Original post by pinkdiamond1001

haha well at least you got more practice through that! :P thanks so much, that makes everything so much clearer! do you happen to know the explanation to this question, the correct answers were the first two but I'm really confused how :s-smilie:

https://www.google.co.uk/search?q=cast+diagram&source=lnms&tbm=isch&sa=X&ei=1B9yUsz5F8yBhAeFwICICg&sqi=2&ved=0CAcQ_AUoAQ&biw=1366&bih=643#facrc=_&imgdii=_&imgrc=ZzlC2wz8yzbjKM%3A%3BS951egCDDUcyYM%3Bhttp%253A%252F%252Fwww.codecogs.com%252Fusers%252F13108%252Fimg_trig_7.jpg%3Bhttp%253A%252F%252Fwww.codecogs.com%252Flibrary%252Fmaths%252Fgeometry%252Ftrigonometry%252Ftrigonometrical-ratios.php%3B507%3B500
ok that's a google link for images of one

you start at the positive x axis and move anticlockwise
if it is between 0 and 90, it will be in the 'A' quadrant which means 'All are positive (sin,tan,cos), then 'S' quadrant which means only sin is positive etc. etc.
so if you have 2 sin angles, and one is in the S quadrant yet the other is in the C (due to differences of 180 only, still same angle), they will just be the same number with opposite signs

Reply 1386

ksi

has anyone done the question about a square conference table? it has a load of shapes in it and i can't seem to get my head round it

Reply 1387

Shivvers

The algebra questions in Section 1 (and 2 for that matter) are killing me. Does anyone know anywhere I can get some practice ones with explanations so that I can work them out more efficiently?

Reply 1388

Razer_M

S1 , 2008, Q25. Lot of people aren't getting this so here's my solution :smile:

The main thing is when the Reds lead decreases by 56, they lose 28 seats and the Blues gain 28.

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Reply 1389

chrisy:)

can u plz help with this:

Reply 1390

Angelica.

A boy is travelling at 10m/s on his bicycle when he brakes and comes to a complete stop 20m later
The combined mass of the boy and the bicycle is 80kg. What force is applied by the brakes?

Reply 1391

Rosine

A ball is thrown vertically upwards and leaves the thrower’s hand with a speed of 12 m/s.
Calculate the height to which it rises. You may assume that all of the initial kinetic energy
of the ball has been converted into gravitational potential energy when the ball reaches its
highest point. (Take the value of g to be 10 N/kg.)

I have no idea where to start ...don't do physics :rolleyes:

thanks!

Reply 1392

Razer_M

Original post by Rosine

thanks!

Quickest way is u^2/20
12*12=144
144/20 = 7.2

You could use mgh=0.5mv^2 but since above is easier and takes about 10 seconds...

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Reply 1393

Rosine

Original post by Razer_M

Quickest way is u^2/20
12*12=144
144/20 = 7.2

You could use mgh=0.5mv^2 but since above is easier and takes about 10 seconds...

Posted from TSR Mobile

Thanks

Reply 1394

ScienceGUYY

Hi could someone help me with this question:

In an experiment concerning radioactive decay, the count rate of radiation 5cm from source X was measured as 140 counts per minute. 12 minutes later, with the detector in the same position, the count rate was measured as 35 counts per minute. Background radiation was recorded as 20 counts per minute.

Calculate the half-life of source X. (Give your answer in minutes).

Thanks

Reply 1395

holly432

Original post by Angelica.

A boy is travelling at 10m/s on his bicycle when he brakes and comes to a complete stop 20m later
The combined mass of the boy and the bicycle is 80kg. What force is applied by the brakes?

You need the equations W=Fs
Kinetic Energy = 1/2mv^2 which is a way of expressing W

and we are told that s = 20

hence F = W/s
= 1/2mv^2/20

Reply 1396

Rosine

Original post by ScienceGUYY

We're told background radiation is 20 so ..we know the count rate actually goes from 120 - 15.

120, 60, 30, 15 <= It has halved 3 times in 12 minutes. So this must have occurred every 4 minutes. Therefore the half- life is 4 minutes :smile:

Reply 1397

SpiralGalaxy

does anybody know how to improve section 1... i keep getting around 4 all the time and i feel absolutely awful :frown:

Reply 1398

originaltitle

Original post by chrisy:)

can u plz help with this:

72 cakes in batches of 12 means 72/12=6 rounds of preparation.
First batch will be completed at 1:00+40min+25min+5min=2:10.
Second batch will be started at 1:40 (we can tell that from the question). Second batch will be put in the oven at 1:40+40=2:20. Add to that 5 minutes to take out the first batch for cooling. 2:20+5=2:25.
You can detect a pattern now: 40 minutes for the first batch and 40+5 minutes for all subsequent batches (5 to take out the previous batch for cooling). You're not adding 25 minutes of any batch because this time is already included in the 40 minutes during which you prepare the next batch.
So 40+(45x6)=265. HOWEVER, the last batch still needs to be in the oven for 25 minutes and then you need to take out of the oven for cooling which'll take you 5 minutes.
So 265+25+5=295. 295/60=hours taken to finish. Don't forget to add that to 1:00 which is when you start.