The Student Room Group

Mechanics 1 Exam question - Help!!

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.

Scroll to see replies

So what have you done so far?
Reply 2
Original post by Mr M
So what have you done so far?


Joined TSR and asked for help :rolleyes:
Reply 3
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
Original post by Mr M
So what have you done so far?


Nothing :tongue:
Reply 5
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
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



Spoiler



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

Spoiler



Spoiler



Spoiler

(edited 12 years ago)
Reply 7
Original post by sr2123
Nothing :tongue:


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=μR F =\mu R to find the the coefficient of friction.
(edited 12 years ago)
Reply 8
How can I work out the values of cos and sin (alpha) using tan (alpha)...sorry, im not understanding this :s-smilie:
Reply 9
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
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
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
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
What would the hypotenuse be?

+ where did you get the numbers 3 & 4?
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
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.
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
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
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
Im not familiar with there being an unknown angle, could someone please go through the question step by step....it's really important that I understand this.

Quick Reply

Latest