Mechanics 1 Exam question - Help!!

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Original post by Mr M

So what have you done so far?

Joined TSR and asked for help :rolleyes:

Reply 3

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Original post by sr2123

A parcel of mass 5kg lies or a rough plane inclined at an angle (alpha) to the horizontal, where tan (alpha) = 3/4. The parcel is held in equilibrium by the action of a horizontal force of magnitude 20N. The force acts in a vertical plane through a line of greatest slope of the plane. The parcel is on the point of sliding down the plane.

a) Find the coefficient of friction between the parcel and the plane.

Have you drawn a diagram and written in all the forces

Reply 4

OP

Original post by Mr M

So what have you done so far?

Nothing

Reply 5

bhogs001

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Original post by Mr M

So what have you done so far?

Can I just say, your help on the GCSE thread was greatly appreciated.

Reply 6

Claree

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Original post by sr2123

A parcel of mass 5kg lies or a rough plane inclined at an angle (alpha) to the horizontal, where tan (alpha) = 3/4. The parcel is held in equilibrium by the action of a horizontal force of magnitude 20N. The force acts in a vertical plane through a line of greatest slope of the plane. The parcel is on the point of sliding down the plane.

a) Find the coefficient of friction between the parcel and the plane.

Draw a diagram with everything you know so far. (include friction)

Hints:

Spoiler

As the particle is in equilibrium, what does this tell you about f=ma=?

Spoiler

(edited 13 years ago)

Reply 7

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Original post by sr2123

Nothing

Use this below diagram:

As the question says that the particle is on the point of moving down the plane, hence the friction will be upwards because friction always opposes motion.

You know that tantheta = 3/4 so you can easily find the values for costheta and sintheta, by making a triangle.

Next, resolve the force perpendicular to the plane to find the normal reaction.

Now, resolve the forces parallel to the plane to find friction. Remember that the particle is in equilibrium hence acceleration is zero.

Next, use

F =\mu R

to find the the coefficient of friction.

(edited 13 years ago)

Reply 8

OP

How can I work out the values of cos and sin (alpha) using tan (alpha)...sorry, im not understanding this :s-smilie:

Reply 9

18

Well, you can use a calculator if you need to

However, as has already been explained, you can draw a right angled triangle and write in the OPPOSITE and ADJACENT from your Tan ratio

Pythagoras will furnish you with the HYPOTENUSE and, therefore Sin and Cos

Reply 10

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Original post by sr2123

How can I work out the values of cos and sin (alpha) using tan (alpha)...sorry, im not understanding this :s-smilie:

See the diagram below:

From the above diagram you can easily find the values of sin and cos. But first find the hypotenuse of the triangle.

Reply 11

Claree

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Original post by raheem94

See the diagram below:

From the above diagram you can easily find the values of sin and cos. But first find the hypotenuse of the triangle.

Just wondering, how do you draw your diagrams on the computer and get them onto a TSR post?

Reply 12

OP

Original post by raheem94

See the diagram below:

From the above diagram you can easily find the values of sin and cos. But first find the hypotenuse of the triangle.

What would the hypotenuse be?

+ where did u get the numbers 3 & 4?

Reply 13

OP

What would the hypotenuse be?

+ where did you get the numbers 3 & 4?

Reply 14

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Original post by sr2123

What would the hypotenuse be?

+ where did you get the numbers 3 & 4?

Do you not know how to use Pythagoras?

You were given Tan = 3/4

Reply 15

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Original post by sr2123

What would the hypotenuse be?

+ where did you get the numbers 3 & 4?

Tantheta equal 3/4. It means that the opposite is 3 and base is 4.
Now use phythagoras theorem to find hypotenuse.

Reply 16

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Original post by Claree

Just wondering, how do you draw your diagrams on the computer and get them onto a TSR post?

You can use any drawing tool (paint is one) and then save as an image ... then use the insert image link above

Reply 17

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Original post by raheem94

Tantheta equal 3/4. It means that the opposite is 3 and base is 4.

Adjacent rather than base :smile:

Reply 18

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Original post by Claree

Just wondering, how do you draw your diagrams on the computer and get them onto a TSR post?

I use adobe photoshop to draw the diagrams. I upload them on imageshack to post here.

Reply 19