Question

A 15.0-kg block is dragged over a rough, horizontal surface by a 70.0-N force acting at 20.0° above the horizontal. The block is displaced 5.00 m, and the coefficient of kinetic friction is 0.300. Find the work done on the block by c) the gravitational force. (d) What is the increase in internal energy of the block–surface system owing to friction? (e) Find the total change in the block’s kinetic energy.

Answer 1

I assume the free body diagram is

Answer 2

frictional force = 44.145N

Answer 3

I messed up my free body diagram

Normal force
15(0) = N + 70sin(20) - 15(9.81)
N = -70sin(20) + 15(9.81)
Normal Force = 123N

Answer 4

Nevermind I solved it :)

Answer 5

My frictional force was wrong :S but I corrected it when I corrected the normal froce I had
d) 184N
e)

Answer 6

that's great! :)

Answer 7

what did u do to find (d) ?

Answer 8

I assume that the graviational and normal force both equal to 0 work, for d I got 144N m

Answer 9

or 144J

Answer 10

I messed up my units oh well

Answer 11

yes, gravitational force does 0 work...since there is no disp in that direction. and the answer to (e) is just the work done in displacing the block by 5m.
but i don't know how to solve for (d)...can u help me there?

Answer 12

Yes not a problem

To find the total change we use equation
K = 1/2mv^2

we need to find velocity so we use the equation

vf = vi + 2a(Delta x)
thus we have

vf = 0 + 2a(5)

now we need to solve for acceleration we can jsut use the force equation
we know that

ma = 70cos(20) - 36.9
=
15a = 70cos(20) - 36.9

the it is as simple as solving for a and then subing vf into the kinetic energy equation

Answer 13

wow internet explorer is horriable, no idea why my school doesnt have fire fox

Answer 14

no...i meant the how to find the increase in the internal energy of the block-surface system because of friction..?

Answer 15

side note: u don't use google chrome?

Answer 16

no I prefer firefox. I found the Normal force to be 123N so then I use that to find the frictional force which is 36.9N
then I jus sub the frictional force into the work equation

W = 36.9N * 5 = 184J

Answer 17

hope that helps I have to leave Im going to be late for my dgd, thanks for confirming for me :)

Answer 18

oh got it! so that's what it means! thanks!
and how come ur friction force came out to be in 30s?
Friction force = u*N = 3*123 = 369 N

Answer 19

u = 0.3

Answer 20

sry!!!! its 0.3! just saw that! my bad!

Answer 21

no problem thanks again

Answer 22

u too!