Need help with energy conservation questions?

Question

A 55 N force pulls an 8.0 kg block up a ramp at a constant speed. The length from position 2 to 1 is 0.159 m and height is 9.5 cm. I've determined the work required to life the block up the ramp (8.7 J), vertically (7.4 J) and the potential energy (7.4 J) now it asks.... what is the work done against friction then pulling the block up the ramp and what is the force of friction acting on the block. I need help with these to questions, mainly knowing what formulas I need to use I can plug in the numbers myself.

Answer 1

As you have calculated the work done pulling it up is
W=Fs=8.75 J
the work to lift it up is 7.46 J so the rest of the work is work against friction W=8.75 J - 7.46 J = 1.29 J ~ 1.3 J

Then you use W=Fs again, with the work of friction as W, to find the force of friction.

Answer 2

Hallo, the energy conservation law ( first law of Thermocynamics) requieres, that the sum of all forms of energy involved in a process is constant.
In your case are involved:

potential energy Epot
work W1/2 done on the system going from state 1 to state 2 and
friction work Wf1/2 , which appears finally as change of the internal energy U2 - U1 of the system, visible in a raise of temperature.

The first law of Thermodynamics states that for a change of state
from 1 to 2 must be

( Epot2 - Epot1) = W1/2.

This is only true if no friction is involved, for so called reversible processes. When friction is involved the work W1/2 is not completely done to the system, because the friction work by the friction force is dissipating in heat, absorbed by the involved masses and raising their internal energy U. Therefore we can write

( Epot2 - Epot1) +(U2 - U1) = W1/2

In your case is

Epot2 - Epot1 = m*g*Delta h

g = 9,81 m/s^2 acceleration due to gravity on earth
Delta h = h2-h1 difference in height

U2 - U1 = Wf U beeing the internal energy of ramp and mass

Finally we get the equation

m*g*(h2 -h2 ) + Ff*l = N*l

From here we can calculate the friction force Ff

Ff = N - m*g*(h2 -h1) /l

Answer 3

friction is a force in the opposite direction of the applied force and is equal to the coefficient of friction*the normal force
the total work done is 55n*.159m=8.745j
from this subtract the 7.4j to get the work done by friction:
8.745j-7.4j=1.345j of work done by friction, divide this by the normal force (sin(angle)*9.8*8kg)to get the coefficient of friction.