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  1. Rumplestiltskin

    Why can't logs have a negative base?

    I understand that taking logs of a negative number isn't possible because no number to any power produces a negative number. But why not a negative base? Say, log-10(100) = 2. Rewritten, -102 = 100, which is accurate. You could suggest that you may as well just ignore the negative because -x2 =...
  2. Rumplestiltskin

    Amplitude and intensity

    1. Homework Statement The light from a bulb shines equally in all directions. If 20W of light is given off, what will the intensity be 12m from the lamp to 2 significant figures? (Consider the shape of the region illuminated if the light hits this surface after travelling 12m in all...
  3. Rumplestiltskin

    Felix Baumgartner's parachute jump from space -- forces and velocities...

    1. Homework Statement a)ii) Calculate the upward force F acting on Baumgartner at this point. (3 marks) total mass of Baumgartner = 95 kg g = 9.8 ms-2 b) Describe the shape of the graph between 30s and 70s. Explain the velocity changes in terms of changes in the air through which Baumgartner...
  4. Rumplestiltskin

    Factorising cubic

    1. Homework Statement The curve C with equation y = f(x) passes through the point (5, 65). Given that f'(x) = 6x2 -10x - 12, a) use integration to find f(x) b) Hence show that f(x) = x(2x+3)(x-4) 3. The Attempt at a Solution I have no problem with this question, except it seems the given...
  5. Rumplestiltskin

    Work done by friction (rolling resistance)

    1. Homework Statement The carriage and its passengers start at rest at A. At B, the bottom of the ride, the maximum speed of the carriage is 20ms-1. The vertical distance between A and B is 110m. The length of the track between A and B is 510m. The mass of the carriage and the passengers is...
  6. Rumplestiltskin

    Distance / speed / time

    1. Homework Statement A car passes through traffic lights as they turn from red to green at a speed of 12ms-1. A motorcyclist, starting from rest, accelerates from the traffic lights in the same direction as the car at 1.5ms-2. After what distance from the lights will they meet? (OPTIONS: 16m...
  7. Rumplestiltskin

    Acceleration and displacement

    1. Homework Statement A car accelerates uniformly from rest along a straight road and experiences negligible frictional forces. The car travels 15m in the second second of its journey. How far does it travel in the fifth second? (OPTIONS: 15m, 35m, 45m, 75m) 2. Homework Equations 3. The...
  8. Rumplestiltskin

    Power and energy

    1. Homework Statement A 55kW motor is used to lift a 4800kg mass vertically up a mine shaft. What is the maximum possible speed that the mass could move upwards? Give your answer to 2 significant figures. 2. Homework Equations 3. The Attempt at a Solution I correctly answered this as 55000...
  9. Rumplestiltskin

    Work done = Fx

    1. Homework Statement A 4.0kg ball is thrown vertically up into the air with an initial velocity of 8.5ms−1 . By the time it is height h metres above the starting point, it has a velocity of 3.0ms−1 and has done 4.0J of work against air resistance. Find h. 2. Homework Equations Work done =...
  10. Rumplestiltskin

    Integrating for area of intersection

    How does it work that you can subtract y2 from y1 and integrate the product within defined limits for the area of their intersection (within those limits)? Maybe that's not the right terminology - you arrive at the area for the region bounded by both functions. Is it just the same in practice...
  11. Rumplestiltskin

    Defined integration general question

    Not a homework problem, so not sure if this is in the right area. Thought it was too sophomore to post in the maths forums. So, when you integrate y within defined limits for x, you get the area between the graph and the x-axis within those limits for x. But a) Why is this always between the...
  12. Rumplestiltskin

    Another moments question

    1. Homework Statement A metre stick has its centre of mass at the 50cm mark, and weighs 0.92N . A 2.00N weight is stuck to the 10cm mark with massless glue. About which point will the ruler balance? 2. Homework Equations Σclockwise = Σanticlockwise 3. The Attempt at a Solution 2 N * 0.4 m =...
  13. Rumplestiltskin

    Moments question

    1. Homework Statement Two workers are moving a 20kg , 10m scaffolding pole. One stands at the end, the other stands 2.0m from the other end. Calculate the force exerted by the worker standing at the end in holding the pole. Assume the mass is distributed evenly and g = 9.8 m/s2. 2. Homework...
  14. Rumplestiltskin

    Roller coaster physics

    1. Homework Statement b) Calculate the maximum velocity of the empty carriage at D. (3 marks) 2. Homework Equations / 3. The Attempt at a Solution 750 x 9.8 = 7350 N No clue. Can't use SUVAT on the vertical plane to find time because v = u = 0 from peak/trough to peak/trough. Horizontal...
  15. Rumplestiltskin

    SUVAT projectile motion

    1. Homework Statement A golfer is about to hit a golf ball from a tee to a hole on the green. The tee and the green are at the same level. The golfer hits the ball, projecting it at a speed of 35 m/s 28° to the horizontal. Air resistance is negligible. Calculate: a) the horizontal distance...
  16. Rumplestiltskin

    Moments metre stick question

    1. Homework Statement A metre stick is pivoted at 50cm and is in equilibrium. There is a 2.0N upwards force at the 5.0cm mark, and a 12N downwards force at the 40cm mark. Force F acts at the 75cm mark. Find force F. Assume the upwards direction is positive. 2. Homework Equations 3. The...
  17. Rumplestiltskin

    Another SUVAT problem

    1. Homework Statement a) How much time does a dropped weight take to fall 120m down a cliff? (I answered this correctly as 4.9s -- √(s/0.5 x g).) b) What would the time be (in question a) if the weight was thrown downwards at 2.5m/s? 2. Homework Equations SUVAT 3. The Attempt at a Solution...
  18. Rumplestiltskin

    SUVAT problem

    1. Homework Statement What is the velocity of a rugby ball 3.0s after it is kicked vertically upwards with a speed of 16m/s? Give your answer to 2 s.f. 2. Homework Equations SUVAT 3. The Attempt at a Solution s = ? u = 16 v = ? a = g = 9.8 t = 3 Erm... v = u + at? 16 + 9.8 x 3 = 45m/s...
  19. Rumplestiltskin

    Projectile motion questions

    Hi all. I just recently dropped psychology for physics so this topic as a whole has me stumped and the textbook isn't helping. I'll be using this thread for any questions that arise pertaining to projectile motion (so more than one), if that's cool? Should be really basic. Thanks. 1. Homework...
  20. Rumplestiltskin

    How y'all doin'

    Hey all, UK student currently studying A-level physics, maths, English lit. and an EPQ (5000 word dissertation, counts for an AS). Hoping to get into UCL's Arts and Sciences course with a specialisation in engineering. Having recently dropped psychology for physics I have some catch up work to...
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