Question 22N.2.SL.TZ0.1
| Date | November 2022 | Marks available | [Maximum mark: 8] | Reference code | 22N.2.SL.TZ0.1 |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Describe, Determine, Explain, State | Question number | 1 | Adapted from | N/A |
A raindrop falls vertically from rest.
The graph shows how the speed of the raindrop varies with time t.
During the first 3.0 s of motion, the raindrop falls a distance of 21 m and reaches a speed of 9.0 m s−1. The mass of the raindrop is 34 mg. The temperature of the raindrop does not change.
State the initial acceleration of the raindrop.
[1]
g OR 9.81 «m s−2» OR acceleration of gravity/due to free fall ✓
Accept 10 «m s−2».
Ignore sign.
Do not accept bald “gravity”.
Accept answer that indicates tangent of the graph at time t=0.
A nice introductory question answered correctly by most candidates. Most answers quoted the data booklet value, with a few 10's or 9.8's, or the answer in words. Very few lost the mark by just stating gravity, or zero.
Explain, by reference to the vertical forces, how the raindrop reaches a constant speed.
[3]
Identification of air resistance/drag force «acting upwards» ✓
«that» increases with speed ✓
«until» weight and air resistance cancel out
OR
net force/acceleration becomes zero ✓
A statement as “air resistance increases with speed” scores MP1 and MP2.
This was very well answered with most candidates scoring 3. The MP usually missed in candidates scoring 2 marks was MP2, to justify the variation of the magnitude of air resistance, although that rarely happened.
Determine the energy transferred to the air during the first 3.0 s of motion. State your answer to an appropriate number of significant figures.
[3]
«loss in» GPE = 3.4 × 10−5 × 9.81 × 21 «= 7.0 × 10−3» «J»
OR
«gain in» KE = 0.5 × 3.4 × 10−5 × 9.02 «= 1.4 × 10−3» «J» ✓
energy transferred to air «=7.0 × 10−3 − 1.4 × 10−3» = 5.6 × 10−3» «J» ✓
any calculated answer to 2 sf ✓
Allow [1] through the use of kinematics assuming constant acceleration.
Allow ECF from MP1.
Generally well answered, although several candidates lost a mark, usually as POT (power of ten) by quoting the value in kg leading to an answer of 5.3 J. Most candidates were able to score MP3 by rounding their calculation to two significant figures.
Describe the energy change that takes place for t > 3.0 s.
[1]
«gravitational» potential energy «of the raindrop» into thermal/internal energy «of the air» ✓
Accept heat for thermal energy.
Accept into kinetic energy of air particles.
Ignore sound energy.
Of the wrong answers, the most common ones were gravitational potential to kinetic or the idea that because there was no change in velocity there was no energy transfer. A significant number, though, scored by identifying the change into thermal (most of them), kinetic of air particles (a few answers) or internal (very few).