• Support PF! Buy your school textbooks, materials and every day products Here!

Help with thermal/kinetic friction energy?

  • #1

Homework Statement


A child whose weight is 269 N slides down a 6.80 m playground slide that makes an angle of 41.0° with the horizontal. The coefficient of kinetic friction between slide and child is 0.190. (a) How much energy is transferred to thermal energy? (b) If she starts at the top with a speed of 0.314 m/s, what is her speed at the bottom?


Homework Equations


ke=1/2 mv2
thermal energy = fkd = fnUkd


The Attempt at a Solution



for b I used 1/2mvi2 + mgh - fkd = fnUkd = 1/2mvf2
and got it correct...
I missed the class where the teacher explained thermal energy and frictional energy so I assumed that the energy lost to friction is turned into thermal energy and i used
thermal energy = fkd = fnUkd
plugged everything in and got 228 J...
but maybe i have the relationship wrong?
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
25,832
251
hi dorkymichelle! :smile:

(have a mu: µ :wink:)
I missed the class where the teacher explained thermal energy and frictional energy so I assumed that the energy lost to friction is turned into thermal energy …
yes, that's correct …

kinetic energy and potential energy are called "mechanical energy", and any "missing" energy (in questions like this) is thermal energy :smile:
 
  • #3
so for a, I should just use equation thermal energy = fnUkd
and I got 228 J but when I put in the answer,(my hw is online) its wrong...
am i reading the question in correctly somehow?
but I got b right.
 
  • #4
tiny-tim
Science Advisor
Homework Helper
25,832
251
hi dorkymichelle! :smile:
so for a, I should just use equation thermal energy = fnUkd
and I got 228 J but when I put in the answer,(my hw is online) its wrong...
i make it the same as you, 228 J (= 269*6.8*sin41°*0.19) :confused:
 
  • #5
hi dorkymichelle! :smile:


i make it the same as you, 228 J (= 269*6.8*sin41°*0.19) :confused:
oops, found the mistake, in finding normal force, its mgCOS41 not Sin. =d silly mistake!
 

Related Threads on Help with thermal/kinetic friction energy?

Replies
20
Views
644
Replies
13
Views
854
Replies
1
Views
5K
  • Last Post
Replies
5
Views
658
  • Last Post
Replies
6
Views
12K
  • Last Post
Replies
6
Views
22K
  • Last Post
Replies
9
Views
684
Replies
2
Views
22K
Replies
2
Views
10K
Replies
6
Views
28K
Top