Kinetic energy and work problem

[J-dizzal]

Homework Statement

In the figure here, a block of ice slides down a frictionless ramp at angle θ=55.0 ˚ while an ice worker pulls on the block (via a rope) with a force that has a magnitude of 54.0 N and is directed up the ramp. As the block slides down through distance d = 0.400 m along the ramp, its kinetic energy increases by 80.0 J. How much greater would its kinetic energy have been if the rope had not been attached to the block?

http://edugen.wileyplus.com/edugen/courses/crs7165/art/qb/qu/c07/fig_7_C.gif

Homework Equations

K=1/2 mv², w=Fd, http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c07/math/math080.gif, http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c07/math/math082.gif

The Attempt at a Solution

The work done in the positive x dir is -21.6 because the box is sliding down, if the kinetic energy is 80J then 21.6J+80J=101.6J is the total. But this is not right.
http://i1164.photobucket.com/albums/q562/falsovero/20150630_163254_zps9et5lfe6.jpg [/B]

 

[SammyS]

Homework Statement

In the figure here, a block of ice slides down a frictionless ramp at angle θ=55.0 ˚ while an ice worker pulls on the block (via a rope) with a force that has a magnitude of 54.0 N and is directed up the ramp. As the block slides down through distance d = 0.400 m along the ramp, its kinetic energy increases by 80.0 J. How much greater would its kinetic energy have been if the rope had not been attached to the block?

http://edugen.wileyplus.com/edugen/courses/crs7165/art/qb/qu/c07/fig_7_C.gif

Homework Equations

K=1/2 mv², w=Fd, http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c07/math/math080.gif, http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c07/math/math082.gif

The Attempt at a Solution

The work done in the positive x dir is -21.6 because the box is sliding down, if the kinetic energy is 80J then 21.6J+80J=101.6J is the total. But this is not right.
http://i1164.photobucket.com/albums/q562/falsovero/20150630_163254_zps9et5lfe6.jpg [/B]

What is the correct answer?

Read the question you're asked carefully.

"How much greater would its kinetic energy have been if the rope had not been attached to the block?"​

 

[J-dizzal]

its would be 101.6 - 80. would be the difference between the the work with the 54N and without?

 

[J-dizzal]

Read the question you're asked carefully.

"How much greater would its kinetic energy have been if the rope had not been attached to the block?"​

thanks i need to work on this, it gets me often.