A crate is pulled by a force (parallel to the incline) up a rough incline. The crate

  • #1
A crate is pulled by a force (parallel to the
incline) up a rough incline. The crate has an
initial speed shown in the figure below. The
crate is pulled a distance of 9.17 m on the
incline by a 150 N force.
The acceleration of gravity is 9.8 m/s2 .
a) What is the change in kinetic energy of
the crate?
Answer in units of J

b) What is the speed of the crate after it is
pulled the 9.17 m?
Answer in units of m/s

For part A i tried
F-mg[sin theta - (friction x cos theta)] and got 135.232 but got wrong answer then i tried multiplying it by the distance and got it wrong.
Also i tried using F - [ μ m g cos θ ] and got it wrong
Someone please help me
 

Answers and Replies

  • #2
Delphi51
Homework Helper
3,407
11


The question appears to be incomplete. Do you know the angle, initial speed and coefficient of friction? If so, your calculation of
"F-mg[sin theta - (friction x cos theta)]"
looks like a good start. Here F = 150, friction = μmg. The result of the calc is the total force on the mass, which you can use in F = ma to find the acceleration. Once you have that, you can use accelerated motion formulas to find the Vf and then the Ek to complete part (a).
 
  • #3


ok i got part a which was

533.0427

how do i get part B
i tried

V= square root 2(553.0427)/11
but got the wrong answer
 
  • #4
Delphi51
Homework Helper
3,407
11


Didn't you find the Vf in part (a) ? Once you found the acceleration, you would have used d = Vi*t + .5*a*t² to find the time and then
Vf = Vi + a*t to get Vf. Only after knowing Vf are you in a position to do the energy calc for the (a) answer.
 

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