A girl places a stick at an angle of 55.0° against a flat rock on a frozen pond. She pushes at an angle and moves the rock horizontally for 2.50 m across the pond at a velocity of 5.00 m/s and a power of 130.0 W. What force did she apply to the stick? How much work did she do? Include all work and a free-body diagram!

***How can I solve this? Thank you!! :)

Question

A girl places a stick at an angle of 55.0° against a flat rock on a frozen pond. She pushes at an angle and moves the rock horizontally for 2.50 m across the pond at a velocity of 5.00 m/s and a power of 130.0 W. What force did she apply to the stick? How much work did she do? Include all work and a free-body diagram!

***How can I solve this? Thank you!! :)

jim_thompson5910 · Answer

ok so this page is quite handy http://www.physicsclassroom.com/calcpad/energy it states that P = F*v*cos(theta) P = power F = force v = velocity theta = angle

anonymous · Answer

okay! :)

jim_thompson5910 · Answer

once you determine F, use it in 

W = F*d*cos(theta)

W = work
F = force
d = displacement
theta = angle

anonymous · Answer

okay:)

so in this case, are these the values?

P=power= 130
F=force= x (unknown)
v=velocity=5
theta=angle=55

and then this?

130=F*5*cos(55)
130=F*5*.5735764364
130=F*2.867882182
F=force=45.3296072

?

anonymous · Answer

i'm not sure if i calculated that right, and also not sure if cos(55)=0.573576?

anonymous · Answer

i was using degrees in the calc!

jim_thompson5910 · Answer

everything looks good

jim_thompson5910 · Answer

yep theta is in degrees

anonymous · Answer

ooh yay! :)

okay, and so from here, i do this?

W=F*d*cos(theta)
work=45.33*2.50*cos(55)

=65.00054965 

so about 65 = work?

anonymous · Answer

and so that's the problem?

force=F=45.3296072

and work=W=65

?  :/

also, i'm not sure exactly, but what would the final units be? I always confuse them :(

jim_thompson5910 · Answer

on that page, it says "the standard metric unit of work is a Newton meter"

jim_thompson5910 · Answer

W = 65 looks good

jim_thompson5910 · Answer

the units for the force are in newtons

anonymous · Answer

ohh okay! 

so 65 N and 45.33 N ?

like that?

jim_thompson5910 · Answer

"the standard metric unit of work is a Newton meter"

not just "newtons"

anonymous · Answer

ohhh

what are the symbols for the newton meter? 

N/m ?

anonymous · Answer

oh oops, just Nm ?

jim_thompson5910 · Answer

yeah just Nm I think

jim_thompson5910 · Answer

oh it also says that 

Joule = Newton meter

jim_thompson5910 · Answer

so work is in joules

anonymous · Answer

ohh okay! joules make sense to me :) 

yay!! so that is all to this problem?: O

jim_thompson5910 · Answer

I think so

anonymous · Answer

okay, yay!! thank you so much!! :) your explanations were so clear!! :D I understand it now:) just need to memorize those formulas!! :D