Chapter 9 Exercise 9A

Chater 9 Exercise 9A Q. 1. 0. 1,000 = 0 kg/m Q. 2. 75 1,000 = 0.75 Q.. (i) 1 m has mass 1.6 1,000,000 = 1,600,000 grammes (ii) = 1,600 kg Density = 1,600 kg/m 1,600 1,000 = 1.6 Q.. Volume = 0.1 0.06 0.02 = 0.00012 m Mass Density = Volume 1.0 = = 9,000 kg/m 0.00012 Relative density = 9,000 1,000 = 9 Q. 5. Volume = Mass Density = 70 90 = 1 1 m Mass = Volume Density = 1 2, = 175 kg 1 Q. 6. s v sv 1 60 60 0.95 0 100 9 _ s = 9 100 = 0.9 Q. 9. Volume = 0. 0. 0.2 = 0.02 m eight = Vrg = (0.02)(1,000 g) = 2g N Q. 10. Volume = r 2 h = (0.0) 2 (0.1) = 0.00009 m eight = Vrg = (0.00009 )(00)g = 0.072 g N Q. 11. (i) V = 1 h(r2 + Rr + r 2 ) = 1 (1)(1 + 5 + 6) = 1,026 cm = 0.001026 m eight = Vrg = (0.001026 )(1,000)g = 1.026g N (ii) V = 1 h(r2 + Rr + r 2 ) = 1 (6)(9 + 2 + 6) = 25 cm = 0.00025 m eight = Vrg = (0.00025)(9)(g) = 0.21g N Mass (iii) Density = Volume 1.026 + 0.21 = 0.001026 + 0.00025 = 1.267 0.0012 = 990 Exercise 9 ecific gravity = 990 1,000 = 0.99 Q. 7. s v sv 7 10 70 9 1 9 11 79 Q.. s v sv 1 100 100 0.9 x 0.9x 100 + x 100 + 0.9x _ s = 79 11 = 7.12 100 + 0.9x = 0.9625 100 + x 100 + 0.9x = 96.25 + 0.9625x x = 60 ml Q. 1. (i) Pressure = hrg = (2)(1,000)g = 2,000g N/m 2 (ii) Thrust = Pressure Area = 2,000g (2) 2 =,000g N eight = Vrg = (2) (1,000)g =,000g N Q. 2. (i) Pressure = hrg = (0.11)()g = 9.5g N/m 2 (ii) Thrust = Pressure Area = (9.5g) (0.05) 2 = 0.275g N (iii) eight = Vrg = r 2 hrg = (0.05) 2 (0.11)()g = 0.275 g N 1

Q.. Thrust = Pressure Area = (hrg)(r 2 ) = (0.1)rg((0.2) 2 ) = 0.0000rg eight = Vrg = 1 h(r2 + Rr + r 2 )rg (b) x 17 x 17 Q.. (a) = 1 (0.1){(0.05)2 + (0.05)(0.02) + (0.02) 2 }rg = 0.0001g The ratio is, therefore, : 1 Pressure at = Pressure at h(1,000)g = ()g h = 6. cm Difference = 6. = 1.2 cm (b) Pressure under mercury = Pressure under oil h(9)g = ()g h = 7.16 cm Pressure at = Pressure at x ()g + (17 x)(1,600)g = 17(1,000)g x = 16. cm Q. 6. Pressure = hrg = ()(1,000)g =,000g N/m 2 Thrust = Pressure Area = (,000g)(2 2) = 12,000g N (i) 2 2 h = 1 1 1 h = 1 m (ii) P = hrg = ( 1 )(1,000)(g) 2g N/m2 (iii) T = P A = (2g)() = 1,000g N Q. 7. (i) R 2 h = r (16)h = (27) h = 2 1 cm = 0.0225 m (ii) P = hrg = (0.0225)(1,000)g = 22.5g N/m 2 (iii) Thrust = P A = (22.5g)( (16)) = 60 N Q. 5. (a) 17 Pressure at = Pressure at h(1,600)g = 17(1,000)g h = 1.25 cm Difference = 17 1.25 = 15.75 cm Q.. (i) R 2 h = r (6)h = (27) h = 1 cm = 0.01 m (ii) P = hrg = (0.01)(900)g = 9g N/m 2 (iii) T = P A = (9g)( (0.06) 2 ) = 0.02 g N Q. 9. 1 dyne cm 2 = 10 5 Newtons 10 = 0.1 N/m2 m2 Q. 10. (i) Thrust = Pressure Area = (hrg)(r 2 ) = (2)(1,2)(9.)( 22 7 ) (1.)2 = 1,920 N = 1.92 kn (ii) Volume = M r = 7 = 0. m 2,0 at x = Increase in deth r 2 x = 0. x = 0. r 2 2

Increase in ressure = hrg = 0. r 2 (1,2)g Increase in thrust = P A = 0. r 2 (1,2)g(r2 ) =,675 N =.675 kn Exercise 9C (i) H2 O = I 5 = = 10 (ii) = I L = () L L = 0. (iii) In liuid, L = 0.75 Aarent t. Q. 1. ouyancy = 12 = = = 12 = Q. 2. 5% 65% = Vrg = ( 65 100 ) V (1,000)g = 6Vg ut = r = 6 = 0.65 Q.. 0.9, as in the last uestion Q.. = 1 15 = = = 1 = 6 = 1 16 = 2 w 2 () L = 2 Q. 5. (i) = = 0 6 = 5 Aarent weight = 0 5 = 25 N (ii) = (0.9)(5) =.5 Aarent weight = 0.5 = 25.5 N Q. 6. ( ) ( = 1.6 200 17 ) = 160 Aarent weight = 200 160 = 0 N Q. 7. Note: H2 O = ouyancy in water AIR H 2 O = ouyancy in liuid I = Immersed weight = ecific gravity of object L = ecific gravity of liuid 5 = H2 O 5 OIL = 6 Aarent t. = Aarent t. = I L Aarent t. = 0.75 () = 6.25 N Q.. ouyancy in water, = 0 60 = 20 ouyancy in oil, = 0 6 = 16 16 (20) L = 0. Q. 9. (i) V = r = (0.) = 0.06 m OR (ii) = rvg Q. 10. V = r2 h = 2,0 ( 9 2 ) g = 90g N 9 2 m (iii) A. t. = eight ouyancy, = I = 90g 90g 2.5 = 5g N r = 0., h = 0.7 (i) V = 22 (0.) 2 (0.7) 7 V = 0 m OR V = 0.066 m (ii) = rvg =,000 ( 0 ) 9. = 5,17. N

(iii) H2 O = I = 517. = 66.6 A. t. = eight ouyancy = 517. 66.6 = 527.6 N Q. 11. Let = the weight of the body. Let = ouyancy in water. 1 = ouyancy in liuid 1 = (0.) 2 = 0. imilarily, = 0.75 5 2 = 5( 0.) ( 0.75) = = 1 QED Exercise 9D Q. 1. of volume under water = r = 1,000 = 7 = Vrg = (0.1)(7)g = 75g = = 75g = 100g = + T 100g = 75g + T T = 25g Q. 2. Its secific gravity is 0., as in uestion 1 Let V = its volume, xv = volume under the liuid = Vrg = V(00)g = 00Vg = xv(1,200)g = 1,200xVg xv ince it is in euilibrium, = 00Vg = 1,200xVg x = 2 1 1 of its mass, or %, is above the surface. Q.. (i) 0.1 0.9 ( ) of the immersed art. where = weight = (1.1) ( 0.9 ) = 0.99 ince it is in euilibrium 0.1 + 0.9 = = 0.99 = 0.99 (ii) 0.99 of its mass will be below, as in uestion 2. Q.. Its secific gravity is, as in uestion 1. Mg = 20g Let M = the mass of the glass = s L ( ) = (0.)( 20g 0.75 ) = 21 1 g = Mg + 20g 21 1 g = Mg + 20g M = 1 1 kg Q. 5. = 60 0 = 0 = 0 = 60 = 12. It is lead

Q. 6. xv (iii) = 12.5g, = g = T + T = 12.5 =.5g =. N Let V = its volume, xv = volume under the sea. = weight of liuid dislaced = (xv)(1,00)g = weight of the object = V(900)g ince =, xv(1,00)g = V(900g) x = 0.7 Answer: 7% Q. 7. V = (0.)(0.6)(0.) = 0.192 m Q.. = Vrg R = (0.192)(2,0)g = 0g = (0.192)(1,000)g = 192g + R = 192g + R = 0g (i) V = M r R = 2g = 2,22. N T = 12.5 2,0 (ii) M = Vr = 0.005 m = 0.005(00) = kg Q. 9. (i) V = (0.1)(0.2)(0.0) (ii) = 0.0016 m M = Vr a w 1 = 0.0016r r = 625 = 625 1,000 = 5 5 th of its length is submerged Deth = 5 20 = 12.5 cm Q. 10. = 0 5 = 5 = 5 = 0 = Q. 11. Total area = (0 60) + 2(0 0) + 2(60 0) 0 60 = 16,000 cm 2 = 1.6 m 2 0 Volume = 1.6 0.0015 eight = Vrg = 0.002 m = (0.002)(,000)g = 19.2g Let X = the deth of the tank in the lake. = weight of liuid dislaced = (0.6 0. X)(1,000)g = 0Xg = 0Xg = 19.2g X = 0.0 m = cm 5

Q. 12. Pressure at 5 cm = hg = (0.05)(900)g = 5g Pressure at 9.5 cm = (0.05)(900)g + (0.05)(1,000)g = 90g Pressure at 9.5 cm = Twice ressure at 5 cm Pressure at cm = (0.0)(900)g = 27g 5 times ressure at cm = 15g Let x = the deth (in metres) Pressure = (0.05)(900)g + (x 0.05)(1,000)g = 15g 5g + 1,000g g = 15g x = 0.1 m = 1 cm 0.05 x Q. 1. Let A = Atmosheric ressure Pressure at 1 m = 2 Pressure at 2 m A + 1(1,000)g = 2(A + 2(1,000)g) A = 10,000g = 9,000 N/m 2 Q. 1. (i) ouyancy = weight of liuid dislaced (ii) Pressure = hrg (iii) = ( 2 (1) ) (1,000)g = 2,000 g N = (2)(1,000)g = 2,000g Thrust = P A = Fu Fd = (2,000g)((1) 2 ) = 2,000g N 2,000 g = 2,000g Fd Fd =,000 g N Q. 15. (i) ouyancy = weight of dislaced liuid = ( 1 (2)2 (6) ) (900)g = 7,200 g N (ii) Pressure = hrg = (7)(900)g = 6,00g N Thrust = P A = (6,00g)((2) 2 ) = 25,200 g N (iii) = Fu Fd 7,200 g = 25,200 g Fd Fd = 1,000 g N Q. 16. h R ince r 2 = 1 (R2 ), R = 2r Volume = 1 h{(2r)2 + (2r)r + r 2 } = 7 hr2 eight = Vrg = 7 hr2 rg 6

Pressure at base = hrg Thrust = P A = (hrg)((2r) 2 ) = hr 2 rg Ratio, Thrust : eight = hr 2 rg : 7 hr2 rg = 12 : 7 Q. 17. (i) P = hrg = ( 1 2 )(1,000)g = 0g N/m2 (ii) T = P A = (0g) ( ( 1 ) 2 ) = 125 16 g N (iii) = Vrg (ii) (iii) 0.01 Oil ater 0.6 0.6 Mercury Pressure at = Pressure at (0.6)(1,000)g = (0.01)rg + (0.6)(1,600)g r = 01.6 kg/m ater 0.6 h Oil = 1 ( 1 2 ) { ( 1 2 ) 2 + ( 1 2 ) ( 1 ) + ( 1 ) 2 } (1,000)g = 75 16 g eight = 7 T 1 Q. 1. Relative density of the wood = = 0.75 Volume = M r = 7 = 1 10g 15 m Q. 20. (0.6)(1,000g) = h(01.6)g h =.7 cm = 7 mm r r r g = g + 10g = 60g = eight of liuid 60g = ( 1 15 ) rg r = 60 15 = 900 s = 0.9 Q. 21. (i) Pressure = hrg = rrg Thrust = P A = rrg(r 2 ) = r rg N (ii) = Vrg = ( 1_ r2 (r))rg = r rg = Fu Fd r rg = Fu r rg Fu = 2r rg N 1 ater Q. 19. (i) M = rv = 1,600 ( 1 2) = 6. tonnes = 6,00 kg 2 Mercury = Vrg = (v 1 + v 2 )(7,00)g = 7,00(v 1 + v 2 )g 1 = v 1 (1,000)g = 1,000v 1 g 2 = v 2 (1,600)g = 1,600v 2 g 7

ince the body is in euilibrium 1 + 2 = 1,000v 1 g + 1,600v 2 g = 7,00(v 1 + v 2 )g Exercise 9E Q. 1. (i) Q. 2. (i) 1 5,00v 2 = 6,00v 1 v 1 v2 = 5 6 = 29 1 F + s = 2 1 1 1 1 1 2 Taking moments about : 2 () = F(5) F = 2 5 (ii) 1 2 5 + = T = 5 = 5 9 2 2 2 1 1 1 1 1 (ii) 1 T + 2 = 2 (Taking moments about t) t ater 2 (2) = T() T = 1 ( = ) (iii) 1 1 + 2 = 2 = = 2 F Q.. Q.. T 1 1 2 Oil T2 ater 1 1 1 1 1 1 1 1 = 1 = = ( ) 2 = (0.9) ( ) _ = 1 + 9 10 = T 1 + + + T 2 T 1 + T 2 = 7 0 9 10 2 (Taking moments about the lower end) (1) + 9 10 (5) = (1) + (5) + T 2 () T 2 = 5 T 1 = 7 0 5 = 1 20 x 2 x x 2 1 x 2 1 x 2 (1 x) Let = the weight of the rod. Let x = the length of the submerged art. = = x 0.6 = 25x 9 1 25x + F = 9 2 (Taking moments about ). (1 x) ( x 2 + 1 x 2 ) ( = F x 2 + 1 x ) (1 x) ( 1 2 ) ( = F 1 x 2 ) F = (1 x) 2 x F

Q. 5. Putting this result into euation 1 gives: 25x (1 x) + = 9 (2 x) 9(2 x)... Multily by 25x(2 x) + 9(1 x) = 9(2 x) 25x 2 x + 9 = 0 (5x 1)(5x 9) = 0 x = 1 5 m (x = 9 m is too long) 5 Answer: 20 cm is submerged. T 1 2 1 2 2 1 1 1 1 1_ = 1 = 2 6 = 12 ( V s ) = 0. ( 1_ T 1 + 12 + 15 + T 2 = T 1 + T 2 = 51 60 T 2 2 ) = 6 15 (Taking moments about the lower end). 1 + 15 () + T 2 () = 2 (1) + 2 () T 2 = 10 20 T 1 = 51 60 10 20 = 101 20 Oil ater Q. 6. (i) 15 10 15 5 7 10 Let x and y be the horizontal and vertical comonents of the reaction at, x = 0 since no other forces act along the vertical. Therefore, the reaction at is vertical. e shall henceforth call it R. (ii) = 10 = = 10s 1 10 + R = 2 (Taking moments about ) 7 () = R(65) 10 R = 7 1 Putting this into euation 1 gives: 10 + 7 1 = 10 = 6 1 = 9 60 = 1 20 y x 20 9