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# M1 Resolving Forces watch

1. Can anyone help me with this question?

A sack of mass 8kg is being pulled up a ramp inclined 20 degrees to the horizontal by a force of magnitude 45N acting parallel to a line of greatest slope of the ramp. The acceleration of the sack is 1.4m/s^2. Find the frictional force.
2. The first step to questions like these is to draw a good diagram with all of the relevant information on it. Could you perhaps provide us with a picture of your diagram?
3. Here's my interpretation. Not sure I've drawn in the Action force correctly though.
What does it mean by parallel to the line of greatest slope of the ramp?
Attached Images

4. Just did some working out and came up with this

Does this look right?
5. (Original post by CodgerCollins)
Just did some working out and came up with this

Does this look right?
You should be using F=ma parallel to the slope and taking up the slope as positive.

Forces are not equal as the sack is not in equilibrium.
6. (Original post by Muttley79)
You should be using F=ma parallel to the slope and taking up the slope as positive.

Forces are not equal as the sack is not in equilibrium.
Could you expand on what you mean by "F=ma parallel to the slope"?
7. (Original post by CodgerCollins)
Could you expand on what you mean by "F=ma parallel to the slope"?
Which force is pulling the sack up the slope? 45N

Which forces are resisting the motion? ..

Have a go and I'll give you the next hint.
8. So the resisting forces would be the frictional force, the weight(w(sin(20)). Would the normal contact force act as a resistive force??
9. (Original post by CodgerCollins)
So the resisting forces would be the frictional force, the weight(w(sin(20)). Would the normal contact force act as a resistive force??
Normal contact force is acting perpendicular to the slope so has no effect parallel to the slope.

Now we know the accel and the forces can you use F=ma now?
10. Like this?
Attached Images

11. (Original post by CodgerCollins)
Like this?
Yes - you know the mass of the sack so just solve to find friction.

[Try to quote an answer then I see you have posted again]
12. Thanks for the help! (Sorry took so long to answer :/ )

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