RVHS_H1_PHY_P2_Solutions

River Valley High School Pg 1 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016 H1 Prelim 2 (2016) Paper 2 Solutions 1 To estimate the frictional force acting on a truck, the driver puts his truck at the neutral gear (not stepping on the accelerator nor applying any brakes) while moving on a level road. He finds that the speed slows down from 24 km h 1 to 18 km h1 over a distance of 10.5 m. The truck is of mass 1500 kg. (a) (i) Show that the frictional force acting on the truck travelling on the level road is 1400 N. v2 = u2 + 2 as (18000/3600)2 = (24000/3600)2 + 2a(10.5) a =  0.926 f = ma = (1500)(0.926) = 1388 = 1400 N (shown) [1] (ii) Hence or otherwise, determine the power developed by the truck’s engine when it is travelling at a constant speed of 12 m s 1 on the level road . The frictional force can be assumed to be constant. P = fv Constant speed, driving force (from engine) = friction = (1400)(12) = 16800 power = …………………………. W [2] (b) The truck then moves up a gentle slope of 1.0  as shown in Fig. 1 .1. The frictional force acting on the truck along the slope is 800 N. Fig. 1.1 Applying the same power from the engine as (a)(ii), determine the maximum speed that the truck can attain up the slope. Pengine = Pfriction + WD against gravity / t 16800 = 800 v + mg h /t = 800 v + mg d sin 1 /t = 800 v + mg v sin 1 v = … = 15.9 = 16 speed = …………………………. m s1 [3] 1.0  Not to scale

River Valley High School Pg 2 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016 2 An air-rifle pellet of mass 2.0 g travels horizontally towards a stationary clay block of mass 56 g. The pellet reaches the block with a speed of 140 m s –1 and remains in the block after the collision. Fig. 2.1 (a) State the principle of conservation of momentum. Total momentum of a system of objects remains constant provided no resultant external force acts on the system. ..………………………………………………………………………………………….. [1] (b) Assuming that the total momentum of the pellet and the block is conserved during the collision, calculate the initial speed of the block after impact. m1u1 = (m1+m2)v (2)(140) = (2+56) v v = 4.8 m s–1 speed = …………………… m s–1 [2] (c) The variation of the momentum of the pellet p with time t is shown in Fig. 2.2. below. The duration of impact (collision) is indicated in the figure. Sketch the variation of the momentum of the block only with time before, during and after the collision. Values of the momentum are not needed in the sketch. [2] Fig.2.2 block pellet block and pellet move together after collision 0 p t Duration of impact

River Valley High School Pg 3 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016 [Turn over