A Level Homework and Answers

Wednesday, May 24, 2017

Tuesday, May 23, 2017

y12 Young's slits questions

3. (a) (i) constant phase difference
(allow 1 mark for same phase difference or same frequency/wavelength) B2

(ii) path difference = λ/2 B1

(b)     (i)      evidence shown that fringe width x = 8.0 mm                                           B1
a = λD/x = 6.4 × 10–7 × 1.5/8.0 × 10–3 = 1.2 × 10–4 m                               C1
(give 2 marks for using x = 4.0 mm giving a = 2.4 × 10–4 m)                    A1

(ii) maximum intensity when y = 0 AND minima at +4 and –4 B1
correct repeat distance, i.e. 8.0 mm with at least 2 full cycles drawn B1

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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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