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Well i am finding this question difficult

A very heavy sack is hung from a rope and pushed sideways. When the sideways push is 220N the rope supporting the sack is inclined 18 degrees to the vertical

(a) Calculate the tension in the rope
(b) Hence find the mass of the sack

Help Please :confused:

Reply 1

Henerz

Have you tried anything? If so, what? If not, try something and post it. In the mean time, try drawing a diagram (important for pretty much any mechanics question) See what equations you can set up from the diagram.

Remember: the system is in equilibrium (theres no acceleration) so the forces must balance :smile:

I take it this is AS Physics?

Reply 2

abhit

whats the formula for tension on a rope

?

Reply 3

Drummy

Reply 4

Henerz

abhit

whats the formula for tension on a rope

?

There is no real "formula" for the tension in the rope. Its the realisation that the whole systemis inequilibrium and therefore tension is the unknown force which keeps the other forces balanced out.

At this stage I'm going to hope you have the diagram, showing the "pendulum" with the 3 forces Tension, Weight and the 220N force on it.

Now, this is the way I like to work it out: Forces are vectors, so they can be moved around on the page, provided their magnitude and direction stays the same (Year 10 Maths, yes?) So, I move them around to create a closed shape: The fact the shape is closed indicates the forces balance i.e. the system is in equilibrium. In this case, you will get a triangle with Tension, Weight and 220N as the sides. You also have the 18 degrees in the appropriate place. A bit more Year 10 maths allows you to find Tension, and then Weight, then the Mass :smile:

Good Luck.

Oh, remember the force is Weight, mg, not the mass, m. I always forgot the factor of g!

Reply 5

Theorist

Just to add on what Henerz said without giving too much away:

After you've drawn the diagram, you will need to resolve the forces into their respective horizontal and vertical components.