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2011 Physics+ WEP Soln

# 2011 Physics+ WEP Soln - (b Principal of Conservation of...

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PHYSICS + Solution – Work Energy Power 1

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4 (a) (i) (ii) Block A: T = m A a ––– (1) Block B: W B – T = m B a ––– (2) (1) + (2): W B = (m A + m B ) a 0.50 × 9.81 = (0.30 + 0.50) a a = 6.13 m s –2 (iii) From (1): T = 0.30 × 6.13 = 1.84 N (iv) Using v 2 = u 2 + 2 as , v 2 = 0 + 2 (6.13) (0.50) v = 2.48 m s –1 (v) Using v = u + at , 2.48 = 0 + 6.13 t t = 0.404 s (vi) Resultant force = 0 N, acceleration is zero. Block B: W B – T = 0, Block A: T – F spring = 0 0.50 (9.81) – 360 x = 0 x = 0.0136 m (vii) By conservation of energy, m B gh = 1 2 k x max 2 (0.50)(9.81)(0.50+ x max )= 1 2 (360) x max 2 180 x max 2 – 4.905 x max – 2.4525 = 0 x max = 0.131 m Alternatively, m B gh + 1 2 ( m A +m B ) v 2 = 1 2 k x max 2 0.50(9.81)( x max )+ 1 2 (0.80)(2.48) 2 = 1 2 (360) x max 2 (viii) After the maximum compression of the spring is reached, Block A will move back to its initial position where it comes to a rest momentarily, before moving towards the spring again to start a new cycle. 3 spring 0.50 m Fig. 7 frictionless pulley A B W A N A T T W B

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5 (a) Gravitational potential (energy) to kinetic / movement (energy) /work done
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Unformatted text preview: (b) Principal of Conservation of Energy Energy can be neither created nor destroyed in any process. It can be transformed from one form to another, and transferred from one body to another but the total amount remains constant in a closed/isolated system. (c) Speed of water Power = force × velocity 1.7 × 10 9 = 3.5 × 10 8 × V V = 4.86 m s –1 (d) Explanation Not all the energy of the falling water is transferred to the output power OR system is not 100% efficient OR water is not brought (1) to rest OR friction OR some of the energy is transferred to heat/sound/surroundings. (e) Time Time = ( 29 1 – 3 3 6 s m 390 ) m ( 10 7 × = 17 949 s (= 299 min) (= 5 h) (f) Work done Mass of water = volume × density = 7 × 10 6 × 10 3 = 6.9 × 10 9 kg Work done = force × distance Work done = 6.9 × 10 9 x 9.81 x 500 = 3.43 × 10 13 J 4...
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2011 Physics+ WEP Soln - (b Principal of Conservation of...

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