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# Force/Friction study help watch

1. Need help with these questions please.

1. A box is pulled forward along a frictionless horizontal surface using a rope angled at 20° above the horizontal. The force pulling the block is 250N along the handles. Draw a suitable diagram showing the force in the handles, and its horizontal and vertical components, and use trigonometry to calculate the force parallel to the surface. What is the force in a direction perpendicular to the surface?

2. A rollercoaster carriage weighing 225kg travels down a frictionless roller starting at a height of 18m above the ground. The rollercoaster track goes down to 1m above the ground as it curves back up to a peak at 10m before falling again

Using the conservation of mechanical energy, determine the kinetic energy of the carriage at the lowest point after the start. How fast is the sack travelling when it travels through the lowest point?

How fast will it be travelling as it passes over the next peak?
2. Muss963, what have you tried?
3. Firstly, whoever set these Qs was poorly informed about physics and teaching, and very unreasonably, expects his/her poor students to be mind-readers - where were the "handles" in Q1 AND the "sack" in Q2 "beamed up" from? From Vulcan haha? (REF: Star Trek BBC TV).

Nevertheless, I shall have a shot for you:-

Q1.
Attachment 611664

Sorry pic keeps inverting itself! - you might need to print it or copy and rotate 180 deg

Side AC of Triangle ABC is the actual force at 20 deg to horizontal. Do you agree that side AB is the vertical component (labelled V) and side BC is the H-zontal one (H)?

OK - You know sine of angle is ................................ ........ yes ............................... well done!........................... Opposite/hypotenuse agreed?
OK So from diagram: sin 20 = AB/AC = V/250 So V = 250 X sin 20 Yes?

Then work out BC in a similar way. You are done.

Actually the second part of the Q throws further doubt on the cognitive ability of the examiner!! The direction parallel to the surface is the horizontal direction as the question clearly states that the surface is horizontal and ditto ditto for the perpendicular direction and V. Why does the examiner want you to do exactly the same calculation twice?? Sorry, beats me.!

I am sure you cn do it now - GO ON!
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4. (Original post by macpatelgh)
Firstly, whoever set these Qs was poorly informed about physics and teaching, and very unreasonably, expects his/her poor students to be mind-readers - where were the "handles" in Q1 AND the "sack" in Q2 "beamed up" from? From Vulcan haha? (REF: Star Trek BBC TV).

Nevertheless, I shall have a shot for you:-

Q1.
Attachment 611664

Sorry pic keeps inverting itself! - you might need to print it or copy and rotate 180 deg

Side AC of Triangle ABC is the actual force at 20 deg to horizontal. Do you agree that side AB is the vertical component (labelled V) and side BC is the H-zontal one (H)?

OK - You know sine of angle is ................................ ........ yes ............................... well done!........................... Opposite/hypotenuse agreed?
OK So from diagram: sin 20 = AB/AC = V/250 So V = 250 X sin 20 Yes?

Then work out BC in a similar way. You are done.

Actually the second part of the Q throws further doubt on the cognitive ability of the examiner!! The direction parallel to the surface is the horizontal direction as the question clearly states that the surface is horizontal and ditto ditto for the perpendicular direction and V. Why does the examiner want you to do exactly the same calculation twice?? Sorry, beats me.!

I am sure you cn do it now - GO ON!
Thankyou !!

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