Question 19M.2.HL.TZ1.b.ii
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.2.HL.TZ1.b.ii |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Show that | Question number | b.ii | Adapted from | N/A |
A small metal pendulum bob is suspended at rest from a fixed point with a length of thread of negligible mass. Air resistance is negligible.
The pendulum begins to oscillate. Assume that the motion of the system is simple harmonic, and in one vertical plane.
The graph shows the variation of kinetic energy of the pendulum bob with time.
When the 75 g bob is moving horizontally at 0.80 m s–1, it collides with a small stationary object also of mass 75 g. The object and the bob stick together.
Show that the collision is inelastic.
[3]
initial energy 24 mJ and final energy 12 mJ ✔
energy is lost/unequal /change in energy is 12 mJ ✔
inelastic collisions occur when energy is lost ✔
Candidates fell into some broad categories on this question. This was a “show that” question, so there was an expectation of a mathematical argument. Many were able to successfully show that the initial and final kinetic energies were different and connect this to the concept of inelastic collisions. Some candidates tried to connect conservation of momentum unsuccessfully, and some simply wrote an extended response about the nature of inelastic collisions and noted that the bobs stuck together without any calculations. This approach was awarded zero marks.
