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WJEC GCSE Additional Science Teacher’s Notes 2. Is there a pattern in your results What is the average value of force/acceleration How does this compare to the mass (in kg) of the glider plus slotted masses F/a should be constant with a value (approximately) equal to the total accelerating mass (glider + mass stack). 3. Plot a graph of resultant force (y-axis) against acceleration (x-axis). Confirm that it is a straight line and draw a best-fit straight line through your results (starting at the origin). Student graphs. 4. Measure and calculate the gradient (slope) of the graph. 5. Compare your gradient to the mass (in kg) of the glider plus the slotted masses. Gradient should (approximately) equal total accelerating mass. Questions 8. A fully laden Soyuz spacecraft (mass = 7150 kg) accelerates away from the ISS towards its re-entry point with an acceleration of 2 m/s 2 relative to the ISS. Calculate the resultant force on the Soyuz spacecraft. F = ma = 7150 × 2 = 14 300 N 9. At lift-off, the combined thrust of the SRB and main Shuttle engines is 30 400 000 N. The total weight of the Space Shuttle at lift-off is 20 407 000 N, as its mass is 2 040 700 kg. a Calculate the resultant force on the Space Shuttle at take-off. Resultant force = thrust – weight = 30 400 000 – 20 407 000 = 9 993 000 N b Calculate the acceleration of the Space Shuttle at take-off. F = ma F a m 9 993 000 2 040 700 4.9 m/s 2 10. An astronaut is using the manned manoeuvring unit (MMU) to examine solar panels on the ISS. The MMU generates a small thrust force of 60 N, which accelerates the MMU and the astronaut at 0.25 m/s 2 . Calculate the mass of the MMU plus the astronaut. If the astronaut has a mass of 80 kg, what is the mass of the MMU F = ma F m a 60 240 kg mass of MMU = 240 – 80 = 160 kg 0.25 _ Newton’s second law and momentum_____________ (pages 184–87) Questions 11. During T+200 s and T+300 s of a Space Shuttle launch (i.e. between 200 s and 300 s after launch), the Shuttle (mass = 2 040 700 kg) accelerates from 2600 m/s to 4400 m/s. a Calculate the momentum of the Shuttle at: i T+200 s p = mv = 2 040 700 × 2 600 = 5 306 000 000 kg m/s ii T+300 s p = mv = 2 040 700 × 4 400 = 8 979 000 000 kg m/s b Calculate the change in momentum between these times. 65
WJEC GCSE Additional Science Teacher’s Notes Δp = 8 979 000 000 – 5 306 000 000 = 3 673 000 000 kg m/s c Calculate the resultant force acting on the Shuttle during this time. p F t 3 673 000 000 36 731000 N 100 d During this time, the Shuttle is both gaining altitude and losing mass. Explain how both of these will affect the forces acting on the Shuttle. Weight decreases (Shuttle further from Earth so g decreases, and mass is decreasing). So resultant force increases (thrust remains constant until jettison of tanks and boosters). 12. In preparation for docking with the ISS, a manned Soyuz spacecraft (mass = 7150 kg) changes velocity relative to the ISS from 12.0 m/s to 0.5 m/s. a Calculate the change in momentum of the Soyuz. Δp = mΔv = 7150 × (12.0 – 0.5) = 82 225 kg m/s b Calculate the resultant decelerating force acting on the Soyuz. (No time data given) … assuming change of momentum takes 10 s: p 82 225 F 8222.5 N t 10 c The Soyuz has three ‘retro-rockets’ that are used to decelerate the Soyuz before docking. Explain how these rockets can decelerate the Soyuz. Retro rockets provide thrust force in opposite direction to direction of motion of Soyuz – Newton’s Second Law then gives deceleration. _Touch down! (pages 186–187)___________________ PRACTICAL Making a model of a Soyuz descent module (page 187) Safety: ensure students are safe and stable if they are dropping objects from a height. Provide students with a range of different suitable materials and resources (glue/scissors/ sellotape/tape measures/stopwatches, etc). 66
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