2018 RI H2 Physics P3 solutions

© Raffles Institution 9749/03   2018 Raffles Institution Preliminary Examinations – H2 Physics Paper 3 – Solutions Section A 1 ( a ) ( i ) (The graph is a curve. This implies there is non-constant acceleration due to effect of air resistance. Only at t = 0 is the acceleration equal to g) Draw tangent at t = 0 acceleration = gradient 24.00 1.74 m s2.30  (ii) The Moon’s surface has no atmosphere (very negligible compared to Earth). There is no air resistance outside the container. Read off from tangent (as this is the v-t graph for no air resistance): v = 1.4 m s-1, t = 0.80 s or use equation: v = u + at (substitute value of a from (a)(i), v = 1.4, u = 0) (b) (i) At terminal velocity, resistive force F reaches its maximum value.  max 3 0.0027 1.74 4.70 10 N Fm g     (ii)  3 31 is terminal velocity on Moon)( 1.40 4.70 10 3.36 10 kg s TT vkv mg k k      0.0 1.0 2.0 3.0 4.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 P (a)(i) Q

2    © Raffles Institution 9749/03 (iii)  '' 3' '1 is terminal velocity on Earth)( 3.36 10 0.0027 9.81 7.89 m s TT T T kv mg v v v      ( i v ) 1 . Total mass is 2.5 x initial mass.  3 1 3 2.5 4.70 10 3.50 m s3.36 10 T T kv mg mgv k         Initial gradient is the same, and graph always above the origin al (but below the tangent) – B1 Curve reaches terminal velocity 3.5 m s–1 – B1 (time it reaches terminal velocity is later – not marking pt) 2 . Starts from 4.0 m s–1 Curve must show speed decreasing to vT – B1       2 (a) (i) The gravitational field strength at a point in space is defined as the gravitational force experienced per unit mass at that point. (ii) Gravitational field strength is a vector since it is defined us ing gravitational force which is a vector. (iii) Newton’s law of gravitation states that two point masses attrac t each other with a force that is directly proportional to the product of their mas ses and inversely proportional to the square of the distance between them.  Since gravitational field strength g is defined as the gravitational force acting per unit mass: (b) (i) 22 Sun Jupiter 2 230 7 27 11 6 1.99 10 7.14 10 1.90 10 7.79 10 8.80 10 Sun Jupitersun Sun Jupiter SunJupiter Jupiter GM rrgM gM r GM r              (ii) Since the gravitation field strength due to the Sun on the surf ace of Jupiter is only ~106 (< 0.001%) that of the gravitational field strength on the surface of Jupiter due to its mass, it can be neglected. (c) (i) For a moon in circular orbit about its planet, the centripetal force is provided by the gravitational force acting on the moon by the planet: GF GMm GMg m rm r22 

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