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theone
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Is the book wrong?

A parcel of mass 5kg rests on a rough horizontal floor. The coefficient of friction between the floor and the parcel is 0.2 The parcel is pulled by a rope which is inclined at 10 degrees to the horizontal and the tension in the rope is constant and has magnitude 50N.

a) Find the frictional force.

b) Find the work done by the tension when moving the parcel a distance of 10m.

Given the parcel is initially at rest,

c) Determine the speed of the parcel when it has moved 10m.

The book gets the answer to (a) as 9.8N which seems to me to be obviously wrong. Thoughts?
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mikesgt2
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(Original post by theone)
Is the book wrong?

A parcel of mass 5kg rests on a rough horizontal floor. The coefficient of friction between the floor and the parcel is 0.2 The parcel is pulled by a rope which is inclined at 10 degrees to the horizontal and the tension in the rope is constant and has magnitude 50N.

a) Find the frictional force.

b) Find the work done by the tension when moving the parcel a distance of 10m.

Given the parcel is initially at rest,

c) Determine the speed of the parcel when it has moved 10m.

The book gets the answer to (a) as 9.8N which seems to me to be obviously wrong. Thoughts?
I got 8.06
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mikesgt2
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(Original post by mikesgt2)
I got 8.06
But that was counting the 50sin(10) from the rope. Was I meant to do that?
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cobra
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What book is it in? cos the answers in the books we use are often wrong
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hitmannq8
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Here's what i get:

a) First I had to work out the reaction force R.
R = 5g - 50sin10
= 40.31759

Frictional Force = 0.2 x R
Frictional force = 8.06 N (3 S.F.)

b) Work done = (applied) force X distance
= 50cos10 x 10
= 492 J

(pls correct me if im wrong, the force i used is correct or was i supposed to use the frictional force?)

c) Work done = Increase in Kinetic Energy

as it was at rest.. initial KE was 0.. so final KE = work done..

0.5 x mass x v(squared) = 492
0.5 x 5 x v(squared) = 492
v = 14.0 m/s
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theone
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I agree with both your answers for a.

The book's answer for b is correct (492 J) and for part (c) I get 12.84 ms^-1 which doesn't quite agree with the books 12.6, but i'm close
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theone
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The book's answer is again wrong, it has assumed friction = 9.8 when it isn't as we've agreed.
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