CK-12-Physics - Intermediate

http://www.ck12.org Chapter 6. Work and Energy

Ei=Ef→KEi+PEi=KEf+PEf+Q

Ei= 0 +

1

2

kx^2 and Ef= 0 + 0 +Q=μmgx

Therefore;^12 kx^2 =μmgx,→x= kx
2
2 (μmg)=

( 500 )( 0. 50 )^2

2 ( 0. 20 )( 20 )( 9. 81 )=^1.^59 =^1.^6 m

Check Your Understanding

1. True or False: When dissipative forces are present, the mechanical energy of the system is not conserved.

Answer: True. Dissipative (or non-conservative) forces transfer the kinetic and potential energies of large-scale
objects to small-scale objects such as atoms.

2. True or False: In the presence of non-conservative forces the final kinetic and potential energies of the system can
   never be determined.

Answer:False. In the case where all of the mechanical energy has been transformed into heat we know the resulting
kinetic and potential energies are zero. In cases where we can measure the instantaneous velocity and position of
the objects in the system, the kinetic and potential energies can be found, as well as the energy “lost to heat.”