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WJEC GCSE Additional Science Teacher’s Notes Rocket Launch mass (kg) Launch weight (N) Launch thrust (N) Minimum resultant upwards force at launch (N) Falcon 9 340 000 3 400 000 4 500 000 1 100 000 Soyuz-2 310 000 3 100 000 4 000 000 900 000 _Inertia and Newton’s first law of motion___________ (pages 178–80) PRACTICAL How well does Newton’s first law work on Earth (page 180) 1. Plot a graph of velocity of the glider (y-axis) against distance from the start of the LAT (x-axis). Graph should be linear (horizontal) – apart from the first portion up to the first light gate. 2. Draw a best-fit line through your points. If your glider obeys Newton’s first law then the velocity of the glider will not change as it travels down the LAT and all the velocities will be exactly the same. Graph should be linear (horizontal) – apart from the first portion up to the first light gate. 3. Does your glider obey Newton’s first law This depends on the best-fit line drawn, but probably yes. 4. Why might the velocity of the glider change as it moves down the track Air-resistance could slow the glider down. The air-track needs to be horizontal, otherwise the glider will accelerate/decelerate. 5. Use your data to decide how repeatable this experiment is. Students should plot range-bars on graph to judge the spread of the data. Further experiments: 1. You can introduce more friction into the experiment by turning down the air blower – what happens then Introducing more friction causes the glider to decelerate and slow down. 2. What happens when you increase the inertia of the glider by stacking masses on it Velocity is lower (mass is bigger). Eventually, the extra weight on the glider causes it to come into contact with the LAT, causing friction and slowing the glider down. _ Momentum (pages 180–81)_____________________ Questions 3. Calculate the momentum of a 5 kg toolbag travelling at 7700 m/s. p = mv = 5 × 7700 = 38 500 kg m/s 4. Calculate the momentum of the ISS (mass = 400 000 kg), also travelling at 7700 m/s. 63
WJEC GCSE Additional Science Teacher’s Notes p = mv = 400 000 × 7700 = 3 080 000 000 kg m/s 5. At take-off, the Space Shuttle leaves the launch tower travelling at 45 m/s. The momentum of the Shuttle at this point is 90 000 000 kg m/s. What is the mass of the Shuttle at this point Why isn’t the mass of the Shuttle constant p 90 000 000 p = mv m 2 000 000 kg v 45 As fuel is used up, the mass goes down. 6. When the solid rocket boosters and the external fuel tank are jettisoned, the Space Shuttle has a momentum of 140 000 000 kg m/s, and a mass of 100 700 kg. What is the velocity of the Shuttle at this point p = mv p 140 000 000 v 1390 m/s m 100 700 7. Use the mass and momentum information in these questions and the rest of the text to describe how the mass, velocity and momentum of the Shuttle change during its flight up to docking with the ISS. What is the final momentum of the Shuttle just before docking with the ISS On launch pad before engine on: mass constant, velocity zero, momentum zero At moment of take-off: mass decreasing, velocity increasing, momentum increasing Up to jettison of tanks: mass decreasing, velocity increasing, momentum increasing Orbit just before docking (engines off): mass constant, velocity constant, momentum constant _The forces and motion at take-off (pages 181–84)____ Discussion point A Space Shuttle (mass = 78 000 kg) docks with the ISS (mass = 385 471 kg). At the moment of docking the ISS is effectively stationary and the Space Shuttle is moving at 2 m/s relative to the ISS. What are the relative momentums of the Space Shuttle and the ISS before docking, and what is their combined momentum after docking What is the effective increase in speed of the ISS What does this tell you about momentum and collisions Relative momentum of Space Shuttle = mv = 78 000 × 2 = 156 000 kg m/s Relative momentum of ISS = 0 kg m/s Combined relative momentum after docking = 156 000 kg m/s p 156 000 p = mv v 0.34 m/s m (78 000 385 471) Momentum is conserved during collisions. PRACTICAL Investigating Newton’s second law (pages 182–83) This experimental demonstration works best using data-logging software that calculates acceleration directly. Remember to pre-load the glider with weights that can be transferred to the mass stack so that the total accelerating mass remains constant. 1. Calculate values of force/acceleration in your table and record them. Calculated values will depend upon data obtained. 64
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