/sci/ - Science & Math

[Anonymous No.4493924]

2. A box of mass 2kg is pushed up a smooth plane by a horizontal force of magnitude 20N. The plane is inclined to the horizontal at an angle x, where tanx = 3/4.

Find (a) the normal reaction between the box and the plane

Teacher not here to help, I need to rely on you guys to help please, I tried solving it but I do not get 27.7N as the answer

[Anonymous No.4493935]

i find these questions easy but need a diagram and i cannot be bothered to draw one

[Anonymous No.4493950]

>>4493935
>>4493935
okay i finished drawing now help please, this is op

[Anonymous No.4493958]

yeh, this works out
inverse tan 3/4 to find the angle (its 36.87)
then add the force vectors of the weight and the pushing force to find the reaction force.
http://www.wolframalpha.com/input/?i=20sin36.87%2B%282*9.8%29cos36.87

[Anonymous No.4493967]

>>4493958

>Not expressing tan in terms of sin and cos instead of dealing with inverse functions and decimals

stay highschool EK.

[Anonymous No.4493970]

I get 28 N.

Then again, I use g = 10m/s^2.
Juggling 9.81 isn't really the point of these exercises.

[Anonymous No.4493979]

>>4493967
inverse tan of 3/4 comes out nicely (i actually remembered that it stops at 2 decimal places but i couldnt remember it exactly)

also, im not a math major, but out of curiosity, whats the method if you keep it in terms of tan?
show your method plz?

[Anonymous No.4493986]

>>4493970
yah, that'll be correct
i used 9.8

[Anonymous No.4493996]

>>4493950
2g cos x + 20 sin x = 2g 3/5 + 20 4/5 = 27.76

[Anonymous No.4493999]

>>4493979

Combining tan = sin/cos and sin^2+cos^2=1 you get

<div class="math">\cos x = \frac{1}{\sqrt{1+\tan ^2x}}</div>

By taking the inverse and leaving it at 36.87 you are comiting unecessary rounding errors that werent supposed to exist in the first place. hope it helps

[Anonymous No.4494008]

>>4493996
whoops got 3/5 and 4/5 mixed up. reverse them

[Anonymous No.4494010]

>>4493999
erm...seems more complicaed to me than necessary

also, o rounding erros, seeing as inverse tan of 3/4 is EXACTLY 36.87

(..i did round 'g' tho)

[Anonymous No.4494015]

>>4493999
erm...seems more complicated to me than necessary

also, no rounding errors, seeing as inverse tan of 3/4 is EXACTLY 36.87

(..i did round 'g' tho)

[Anonymous No.4494016]

>>4493999
i would just draw a 3 4 right triangle and use pythag to get 5 hypotenuse

[Anonymous No.4494017]

>>4493979
That tan of 3/4 implies a 3-4-5 triangle. Both the horizontal applied force and the weight of the mass will be represented by a hypotenuse. The resultant normal to the plane in each case is going to be 3/5ths or 4/5ths of the force/weight.

[Anonymous No.4494021]

>>4494016
how the fuck does that help you cockmongling retard!!???

[Anonymous No.4494027]

>>4494016

Yeah, thats actually clever

[Anonymous No.4494034]

this is op, this is what i ve done (2x9.8)/(cos(36.86))=24.5. Now i just don't get how to do the 20N

[Anonymous No.4494036]

>>4494021
because once you have all three sides you can read off trig ratios

also, calm down

[Anonymous No.4494032]

>>4494027
no it fucking isnt.
i mean, yeh, the hypotenuse is 5, but that has FUCKING NOTHING to do with OP's question.

[Anonymous No.4494040]

>>4494032
you need hypotenuse to get sin and cos, defined as opp/hyp and adj/hyp respectively

[le oldfag !9kbJjvwmwE No.4494044]

I wish I knew hard theoretical psychics liek OP ;(

_________________
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We are Legion.
We do not forgive.
We do not forget.
Expect us.

[Anonymous No.4494047]

>>4494032
>>4494021
>EK fails to understand trig yet again

[Anonymous No.4494062]

>>4494036
>>4494040
oh rite, yeh
so its 19.6(4/5)+20(3/5) = 27.68

>also, calm down
yeh, sorry about that :/

[Anonymous No.4494064]

>>4494034
this is totally wrong. why division for instance

[Anonymous No.4494067]

>>4494047
nah i get the trig, i just didnt see why it was necessary, i just though you'd inverse tan and find the angle, and just use that.

[Anonymous No.4494072]

you know what guys, sorry i even started up this question. bye bye, i realise that there examples in the book anyway thanks, this is op

[Anonymous No.4494076]

>>4494062
>yeh, sorry about that
a rare admission of error and contrition on /sci/

this must be respected

[Anonymous No.4494079]

>>4494076
>a rare admission of error and contrition on /sci/
an error in appropriate emotional response, not an error in my method
:/

[Anonymous No.4494081]

>>4494072
meh, kk bye bye

[Anonymous No.4494086]

>>4494079
an error in thinking finding the hypotenuse was irrelevant

but you've blown it now EK