A bead slides on a wire, which is in a vertical plane, as shown in the diagram.

Question

A bead slides on a wire, which is in a vertical plane, as shown in the diagram. Gravity acts in the -y direction. The bead starts at A, moving to the right with an initial velocity v. The wire is frictionless between A and D and between F and G, but there is friction between D and F. (For each statement select True, False, Greater than, Less than, Equal to, or Not enough information to tell.

Between C and D, the speed increases, then decreases
The bead's kinetic energy at B is ... its kinetic energy at F
The speed at B is ... the speed at F
Between D and E, there is positive work done on the bead

- My answers are true, less than, true and greater than. What is the wrong?

Explanation / Answer

1) Between C and D, the speed increases, then decreases:- true because potential energy is converting into kinetic energy.

2) The bead's kinetic energy at B is greater than its kinetic energy at F. because of -ve work of friction

3) The speed at B is greater than the speed at F because there is friction in D to F region which will apply some -ve force

4) Between D and E, there is positive work done on the bead :- Not enough information to tell because if workdone by friction will be equal to the workdone by gravity then workdone will be zero. other wilse work done will be +ve

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