lwymarie said:
ah! the height is 0.5m. I'm so sorry that i forget the type the height in my diagram. would you please help me again now? I'm so sorry..
The missing height is not the only problem. I am going to assume that you meant 4ms^-1 rather than 4ms^-2 at D. If you do that, then here is what MIGHT be true. I'm going to leave some blanks for you to fill in, but the outline covers the things you need to think about.
0.191 N could be the frictional force at the end, but unless the coefficient of friction is different in different places on the track, the frictional force has to change. I will assume the coefficient does change to keep the force constant, and let's see what happens. If the friction is 0.191N, and if the distance from D to the end of motion is 4.19m then the work done by friction from point D on is ____, so the energy at point D would have to be _____
The kinetic and potential energies can be calculated at C and D. If the zero of potential energy is taken to be the bottom of the track, then at C (assuming C is at the very top) the total energy is _____. At D the energy is _____, which is consistent with the assumed frictional force and the runout from point D. The energy lost to friction during the descent from C to D is ______. The distance between C and D is _____, so if you figure out the average force over that distance it comes out to be a bit less than .191 N.
So maybe C is not the top exactly. It's hard to tell from the diagram. If the distance from C to D is a bit less, the frictional force could be .191N, but then the energy at C would be a bit less than what is calculated above. I'm sure I could find a point C that would make the energy loss from C to D just right for a frictional force of .191N
The location of point B is unclear, but if the energy there is to be 1.1J, then the energy loss between B and C has to be _____ (a bit more if point C is located after the top). If the friction is constant, the energy lost from B to C has to be a bit more than the energy loss from C to D, which certainly looks possible.
Unless you have more specific information about the location of the points, then everything else is somewhat speculative. It looks like all three statements MIGHT be true, but the idea of a constant frictional force is unusual. It is more likely that there will be a constant coefficient of friction. You can find the coefficient that would be needed for the force to be .191N at the end. If you use that coefficient and calculate the frictional force from the normal force that could be calculated at C you would find the frictional force to be much greater than .191N. But this is a hypothetical problem, so assuming a constant frictional force is OK. Then it becomes a matter of making sense of the rest of it.
