1 Power is transferred through a machine as shown. power input P I machine. power output P O. power loss P L. What is the efficiency of the machine?

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1 1 1 Power is transferred troug a macine as sown. power input P I macine power output P O power loss P L Wat is te efficiency of te macine? P I P L P P P O + P L I O P L P O P I 2 ir in a bicycle pump is forced troug a valve at a constant pressure p. In one stroke of te pump te volume of air in te pump camber is reduced from V 1 to V 2. V 1 V 2 p initially to valve finally p to valve Wat is te work done on tis air in one stroke of te pump? p(v 1 + V 2 ) 2 p(v 1 + V 2 ) p(v 1 - V 2 ) pv 1 3 ar X is travelling at alf te speed of car Y. ar X as twice te mass of car Y. Wic statement is correct? ar X as alf te kinetic of car Y. ar X as one quarter of te kinetic of car Y. ar X as twice te kinetic of car Y. Te two cars ave te same kinetic.

2 4 trolley runs from P to Q along a track. t Q its potential is 5 kj less tan at P. 2 trolley P Q t P, te kinetic of te trolley is 5 kj. etween P and Q te work te trolley does against friction is 1 kj. Wat is te kinetic of te trolley at Q? 35 kj 45 kj 55 kj 65 kj 5 To travel at a constant speed, a car engine provides 24 kw of useful power. Te driving force on te car is 6 N. t wat speed does it travel? 2.5 m s 1 4. m s 1 25 m s 1 4 m s 1 6 Wic of te following expressions defines power? force x distance moved in te direction of te force force x velocity work done time taken work done x time taken

3 7 Wat is te expression used to define power? 3 output input x time taken force x velocity work done time taken 8 ball is trown vertically upwards. Neglecting air resistance, wic statement is correct? Te kinetic of te ball is greatest at te greatest eigt attained. y te principle of conservation of, te total of te ball is constant trougout its motion. y te principle of conservation of momentum, te momentum of te ball is constant trougout its motion. Te potential of te ball increases uniformly wit time during te ascent. 9 barrel of mass 5 kg is loaded onto te back of a lorry 1.6 m ig by pusing it up a smoot plank 3.4 m long. 3.4 m lorry barrel mass = 5 kg plank 1.6 m Wat is te minimum work done? 8 J 17 J 78 J 17 J 1 Wat is te internal of an object? It is te associated wit te object s movement troug space. It is te associated wit te random movement of te molecules in te object. It is te due to te attractions between te molecules witin te object. It is te sum of all te microscopic potential and kinetic energies of te molecules.

4 11 steel ball is falling at constant speed in oil. 4 Wic grap sows te variation wit time of te gravitational potential and te kinetic of te ball? time time time time 12 stone of weigt 4. N in te Eart s gravitational field is moved from P to Q and ten to R along te pat sown. Q 4 m R 3 m 5 m P Eart's surface How muc potential does te stone gain? 12 J 2 J 28 J 12 J

5 13 n electrical generator is started at time zero. Te total electrical generated during te first 5 seconds is sown in te grap. 5 5 / J time / s Wat is te maximum electrical power generated at any instant during tese first 5 seconds? 1 W 13 W 3 W 5 W 14 concrete cube of side.5 m and uniform density 2. x 1 3 kg m 3 is lifted 3. m vertically by a crane. Wat is te cange in potential of te cube?.75 kj 7.4 kj 29 kj 47 kj 15 In perfectly elastic collisions between two atoms, it is always true to say tat te initial speed of one atom will be te same as te final speed of te oter atom. te relative speed of approac between te two atoms equals teir relative speed of separation. te total momentum must be conserved, but a small amount of te total kinetic may be lost in te collision. watever teir initial states of motion, neiter atom can be stationary after te collision.

6 6 16 Te diagram sows te masses and velocities of two trolleys about to collide. 4 m s 1 2 kg 1 m s 1 4 kg fter te impact tey move off togeter. Wat is te total kinetic of te trolleys after te collision? 1.3 J 12 J 18 J 19 J 17 Wic expression defines power? force distance moved in te direction of te force force velocity work done time taken work done time taken 18 Two equal masses X and Y are moving towards eac oter on a frictionless air track as sown. Te masses make an elastic collision. air track 5 cm s 1 3 cm s 1 X Y Wic row gives possible velocities for te two masses after te collision? velocity of X velocity of Y zero 2 cm s 1 to te rigt 1 cm s 1 to te rigt 1 cm s 1 to te rigt 2 cm s 1 to te left zero 3 cm s 1 to te left 5 cm s 1 to te rigt 19 boat moving at constant speed v troug still water experiences a total frictional drag F. Wat is te power developed by te boat? 1 2Fv Fv 1 2Fv 2 Fv 2

7 7 2 steel ball is falling at constant speed in oil. Wic grap sows te variation wit time of te gravitational potential and te kinetic of te ball? time time time time 21 Te total input E in in a process is partly transferred to useful output U, and partly to tat is wasted W. Wat is te efficiency of te process? U 1 % W W 1 % E in U 1 % E in U + W E in 1 %

8 Two speres and approac eac oter along te same straigt line wit speeds u and u. Te speres collide and move off wit speeds v and v, bot in te same direction as te initial direction of spere, as sown below. before collision u u after collision v v Wic equation applies to an elastic collision? u + u = v v u u = v v u u = v + v u + u = v + v 23 Two balls X and Y approac eac oter along te same straigt line and collide elastically. Teir speeds are u X and u Y respectively. fter te collision tey move apart wit speeds v X and v Y respectively. Teir directions are sown on te diagram. before X u X u Y Y after v X X Y v Y Wic of te following equations is correct? u X + u Y = v X + v Y u X + u Y = v X v Y u X u Y = v X + v Y u X u Y = v X v Y 24 Wic of te following is an expression for power? x time force x displacement force x velocity mass x velocity

9 car driver adjusts te pressure on a car s brakes so tat te car travels at constant speed down a ill from P to Q. P Q Te magnitude of te cange in te car s kinetic is. Te magnitude of te cange in its gravitational potential is. Wic statement is correct? > = > > = 26 n area of land is an average of 2. m below sea level. To prevent flooding, pumps are used to lift rainwater up to sea level. Wat is te minimum pump output power required to deal wit kg of rain per day? 15 kw 3 kw 15 kw 3 kw 27 twig from a tree drops from a 2 m ig cliff on to a beac below. uring its fall, 4% of te twig s is converted into termal. Wat is te speed wit wic te twig its te beac? 35 m s 1 4 m s 1 49 m s 1 63 m s 1 28 mass is raised vertically. In time t, te increase in its gravitational potential is and te increase in its kinetic is. Wat is te average power input to te mass? ( )t ( + )t t + t

10 29 Te kinetic of a particle is increased by a factor of 4. 1 y wat factor does its speed increase? orizontal force of 9 N is used to pus a box across a orizontal floor. Te frictional force on te box is 5 N. Wat is te gain in kinetic of te box wen it is moved troug a distance of 6. m? 24 J 3 J 54 J 84 J 31 cyclist is capable of generating an average power of 3. kw during a 4. km speed trial. His aerodynamic suit and position on te cycle reduce resistive forces to 18 N. Wat is te approximate time acieved in te speed trial? 14 s 24 s 13 s 22 s 32 constant force of 9. kn, parallel to an inclined plane, moves a body of weigt 2 kn troug a distance of 4 m along te plane at constant speed. Te body gains 12 m in eigt, as sown. 4 m 9. kn 12 m 2 kn How muc of te work done is dissipated as eat? 12 kj 24 kj 36 kj 6 kj 33 car wit a total mass of 14 kg is travelling at 3 m s 1. Wat is te kinetic of te car? 21 kj 42 kj 63 kj 126 kj

11 11 34 n object is trown into te air. Wic grap sows ow te potential of te object varies wit eigt above te ground? 35 Te diagram sows a barrel of weigt 1. x 1 3 N on a frictionless slope inclined at 3 o to te orizontal. force of slope on barrel force slope 3 o 1. x 1 3 N barrel force is applied to te barrel to move it up te slope at constant speed. Te force is parallel to te slope. Wat is te work done in moving te barrel a distance of 5. m up te slope? 1. x 1 4 J 2.5 x 1 3 J 4.3 x 1 3 J 5. x 1 3 J In many old-style filament lamps, as muc as 93 J of is emitted as termal for every 7 J of emitted as ligt. Wat is te efficiency of te lamp, as te percentage of electrical converted to ligt? 7 % 8 % 92 % 93 % To get to is office from te entrance of te building, a man as to walk up six fligts of stairs. Te eigt of eac fligt is 2.5 m and te man as a mass of 8 kg. Wat is te approximate gain in te man s gravitational potential during te climb? 12 J 2 J 48 J 12 J

12 12 38 n electric railway locomotive as a maximum mecanical output power of 4. MW. Electrical power is delivered at 25 kv from overead wires. Te overall efficiency of te locomotive in converting electrical power to mecanical power is 8 %. Wat is te current from te overead wires wen te locomotive is operating at its maximum power? car of mass 1 kg first travels forwards at 25 m s 1 and ten backwards at 5 m s 1. Wat is te cange in te kinetic of te car? 2 kj 3 kj 325 kj 45 kj 4 Wen bungee jumping, a student starts wit maximum gravitational potential (position 1), ten falls freely until te rope fully unwinds (position 2), after wic te rope starts to stretc until te lowest point of te jump is reaced (position 3). position 1 position 2 Wat are te kinetic and elastic potential energies at position 3? position 3 kinetic elastic potential maximum maximum maximum minimum minimum maximum minimum minimum

13 13 41 wooden block rests on a roug board. Te end of te board is ten raised until te block slides down te plane of te board at constant velocity v. block v board Wic row describes te forces acting on te block wen sliding wit constant velocity? frictional force on block resultant force on block down te plane down te plane down te plane zero up te plane down te plane up te plane zero 42 Two speres approac eac oter along te same straigt line. Teir speeds are u 1 and u 2 before collision, and v 1 and v 2 after collision, in te directions sown below. before collision u 1 u 2 after collision v 1 v 2 Wic equation is correct if te collision is perfectly elastic? u 1 u 2 = v 2 + v 1 u 1 u 2 = v 2 v 1 u 1 + u 2 = v 2 + v 1 u 1 + u 2 = v 2 v 1

14 43 block of weigt W is pulled up a roug slope by a force F. 14 Wen te block as moved a distance x along te slope, it as risen eigt. x F W Wic expressions give te amount of work done on te block and te amount of gravitational potential gained by te block? work done gravitational potential Fx W F Wx Wx F W Fx 44 n object is trown into te air. Wic grap sows ow te potential of te object varies wit eigt above te ground?

15 45 pendulum bob oscillates between P and R. 15 P R y Q x ssuming te gravitational potential lost in moving from P to Q is converted into kinetic, wat is te speed of te bob at Q? 2 gx 2gx 2 gy 2gy 46 Wic operation involves te greatest mean power? a car moving against a resistive force of.4 kn at a constant speed of 2 m s 1 a crane lifting a weigt of 3 kn at a speed of 2 m s 1 a crane lifting a weigt of 5 kn at a speed of 1 m s 1 a weigt being pulled across a orizontal surface at a speed of 6 m s 1 against a frictional force of 1.5 kn