Question 20N.2.SL.TZ0.1
| Date | November 2020 | Marks available | [Maximum mark: 8] | Reference code | 20N.2.SL.TZ0.1 |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate, Determine, Outline, State | Question number | 1 | Adapted from | N/A |
A company delivers packages to customers using a small unmanned aircraft. Rotating horizontal blades exert a force on the surrounding air. The air above the aircraft is initially stationary.
The air is propelled vertically downwards with speed . The aircraft hovers motionless above the ground. A package is suspended from the aircraft on a string. The mass of the aircraft is and the combined mass of the package and string is . The mass of air pushed downwards by the blades in one second is .
State the value of the resultant force on the aircraft when hovering.
[1]
zero ✓
Outline, by reference to Newton’s third law, how the upward lift force on the aircraft is achieved.
[2]
Blades exert a downward force on the air ✓
air exerts an equal and opposite force on the blades «by Newton’s third law»
OR
air exerts a reaction force on the blades «by Newton’s third law» ✓
Downward direction required for MP1.
Determine . State your answer to an appropriate number of significant figures.
[3]
«lift force/change of momentum in one second» ✓
✓
AND answer expressed to sf only ✓
Allow from .
The package and string are now released and fall to the ground. The lift force on the aircraft remains unchanged. Calculate the initial acceleration of the aircraft.
[2]
vertical force = lift force – weight OR OR ✓
acceleration✓