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Thursday, April 27, 2017

Materials questions

1.       (a)     P.E. at top = 80 × 9.8(1) × 150 = 118 000 (J) (1)
K.E. at bottom and at top = 0 (1)
Elastic P.E. at top = 0, at bottom = P.E. at top for ecf = 118 000 J (1)                    3
  (b)   24 N m–1 × 100 m = 2400 N                                                                               1
  (c)    elastic P.E. is area under F-x graph (1)
graph is a straight line so energy is area of triangle (1)
elastic P.E. = ½ × kx × x = (½kx2) (1)                                                                 2
  (d)   loss of P.E. = 100 × 9.8(1) × 150 = 147 000 J (1)
gain of elastic P.E. = ½ × 26.7 × 1052 = 147 000 J (1)                                          2
  (e)    idea that a given (unit) extension for a shorter rope requires a greater force            1
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  2.     (a)     (i)      speed = d / t                                                                                           C1
          = 24 / 55
          = 0.436 (m s–1) allow 0.44                                                             A1
       do not allow one sf
(ii)     kinetic energy = ½ m v2                                                                         C1
                      = 0.5 ´ 20 ´ (0.436)2
                      = 1.9 (J) note ecf from (a)(i)                                              A1
(iii)    potential energy = mg h                                                                          C1
                         = 20 ´ 9.8 ´ 4
                         = 784 (J)                                                                       A1
penalise the use of g = 10
  (b)   (i)      power = energy / time or work done / time                                               C1
          = (15 ´ 784) / 55
note ecf from (a)(iii)
          = 214 (W)                                                                                    A1
(ii)     needs to supply children with kinetic energy                                            B1
air resistance                                                                                          B1
friction in the bearings of the rollers / belt                                                B1
total mass of children gives an average mass of greater than 20 kg            B1
Max B2

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1.       (a)     (i)      Stress = force / area                                                                                C1
force = stress ´ area
 = 180 ´ 106 ´ 1.5 ´ 10–4
 = 27000 (N)                                                                                  A1
(ii)     Y M = stress / strain                                                                               C1
= 180 ´ 106 / 1.2 ´ 10–3 or using the gradient                                   C1
= 1.5 ´ 1011 N m–2                                                                         A1
  (b)   brittle
elastic/ graph shown up to elastic limit
obeys Hooke’s law / force α extension / stress α strain
no plastic region                                                                                              B3
MAX 3
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4.       cast iron:     brittle
                   brittle explained as having no plastic region
                   elastic
                   elastic explained as returning to original length when
                   the load is removed / linear graph / Hooke’s law obeyed
                   or equivalent words                                                                         MAX 3
          copper:       ductile
                   ductile explained as can be formed into a wire
                   initially elastic
                   plastic where it stretches more and more with little
                   increase in stress
                   plastic explained as does not return to its original length
                   when the load is removed
                   reference to necking at the end                                                         MAX 3
          polythene:   easy to deform / deformed with a small force
                   plastic
                   ductile
                   polymeric                                                                                       MAX 2
                                                                                                                                  MAX 8
          QWC:        spelling, punctuation and grammar                                                      B1
                   organisation and logic                                                                           B1
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