Heat lost by naphthalene
T = 100-80=20k
H1 = 0.5kg x 2100JK/g/K x 20K = 2100J
Lf = mLf = 0.5kg x 170000J/Kg = 85000J
T = 80 -20 = 60k ,
H2 = 0.5kg x 2100J/Kg/K x 60k = 63000J
Heat lost by aluminium
T = 100 – 20 = 80k
H = 0.4kg x 900J/Kg/K x80k = 28800J
Total heat lost = 169000J + 28800J = 197800J
= 197.8KJ
= 198KJ
sharon kalunda answered the question on April 2, 2019 at 08:23
- An electric heater 1KW 240V is used to raise the temperature of a 5kg copper block from 15oC to 33oC. If the specific heat capacity...(Solved)
An electric heater 1KW 240V is used to raise the temperature of a 5kg copper block from 15oC to 33oC. If the specific heat capacity of copper is 400J/Kg/K and assuming no heat is lost to the surrounding,Calculate the time taken.
Date posted: April 2, 2019. Answers (1)
- Explain why steel feels colder than wood at the same temperature.(Solved)
Explain why steel feels colder than wood at the same temperature.
Date posted: April 2, 2019. Answers (1)
- Figure below shows a test tube partially filled with water. An ice wrapped in wire gauze is placed at the bottom of the test-tube. It...(Solved)
Figure below shows a test tube partially filled with water. An ice wrapped in wire gauze is placed at the bottom of the test-tube. It is then held in the flame of a bunsen burner as shown below
State and explain what will be observed after some time
Date posted: April 2, 2019. Answers (1)
- The figure below shows two identical thermometers. Thermometer A has a blackened bulb while thermometer B has a silvery bulb. A candle is placed equidistant between...(Solved)
The figure below shows two identical thermometers. Thermometer A has a blackened bulb while thermometer B has a silvery bulb. A candle is placed equidistant between the two thermometers.
State with a reason the observations made after some time
Date posted: April 2, 2019. Answers (1)
- Figure below shows a cross-section of a vacuum flask (i) Name the parts labelled A and B on the diagram...(Solved)
Figure below shows a cross-section of a vacuum flask
(i) Name the parts labelled A and B on the diagram
(ii) Explain how the heat losses are minimized when hot liquid is poured into the flask
Date posted: April 2, 2019. Answers (1)
- A jet delivering 0.44g of dry steam per second, at 100oC is directed on to crushed ice at 0.0oC contained in an unlagged copper can...(Solved)
A jet delivering 0.44g of dry steam per second, at 100oC is directed on to crushed ice at 0.0oC contained in an unlagged copper can which has a hole in the base. 4.44g of water at 0.0oC flow out of the hole per second.
(i) How many joules of heat are given out per second by condensing steam and cooling to 0.0oC of water formed?(Latent heat of vaporization of steam = 2.26 x 106JKg-1,c for water = 4200JKg-1K-1)
(ii) How much heat is taken in per second by the ice which melts?
(iii) Suggest why these amounts above are different
Date posted: April 2, 2019. Answers (1)
- A block of metal of mass 150g at 100oC is dropped into a logged calorimeter of heat capacity
40J/k containing 100g of water at 25oC. The...(Solved)
A block of metal of mass 150g at 100oC is dropped into a logged calorimeter of heat capacity
40J/k containing 100g of water at 25oC. The temperature of the resulting mixture is 34oC.
(Specific heat capacity of water = 4200J/KgK)
Determine;-
(i) Heat gained by calorimeter
(ii) Heat gained by water
(iii) Heat lost by the metal block
(iv) Specific heat capacity of the metal block
Date posted: April 2, 2019. Answers (1)
- 200g of a solid was uniformly heated by a 0.2 kw heater for sometime. The graph in the figure below shows how the temperature of...(Solved)
200g of a solid was uniformly heated by a 0.2 kw heater for sometime. The graph in the figure below shows how the temperature of the solid changed with time.
(i) Explain what is happening between OA and AB.
(ii) Calculate the specific heat capacity of the solid.
(iii) Calculate the specific latent heat of fusion k of the solid.
Date posted: April 2, 2019. Answers (1)
- A block of metal of mass 300g at 1000c is dropped into a logged calorimeter of heat capacity40Jk-1, containing 200g of water at 200c. The...(Solved)
A block of metal of mass 300g at 1000c is dropped into a logged calorimeter of heat capacity40Jk-1, containing 200g of water at 200c. The temperature of the resulting mixture is 340c
Determine:
(i) Heat gained by calorimeter.
(ii) Heat gained by water.
(iii) Heat lost by the metal block.
(iv) Specific heat capacity of the metal block.
Date posted: April 2, 2019. Answers (1)
- A mass of 2kg is attached to a string of length 50 cm. It is whirled in a circle in a vertical plane
at 10 revolution...(Solved)
A mass of 2kg is attached to a string of length 50 cm. It is whirled in a circle in a vertical plane
at 10 revolution per second about a horizontal axis. Calculate the tension in the string when the
mass is at the :-
(a)Highest point of the circle.
(b) Lowest part of the circle.
Date posted: April 2, 2019. Answers (1)
- A wooden block of mass 200g is placed at various distances from the center of a turntable,which is rotating at constant angular velocity. It is...(Solved)
A wooden block of mass 200g is placed at various distances from the center of a turntable,which is rotating at constant angular velocity. It is found that at a distance of 8.0cm from the center, the block just starts to slide off the table. If the force of friction between the block and the table is 0.4N, Calculate:
(i) The angular velocity of the table
(ii) The force required to hold the block at a distance of 12cm from the center of the table
Date posted: April 2, 2019. Answers (1)
- A small pendulum bob having a mass of 150g is suspended by an inelastic string of length 0.5m. The mass is made to rotate in...(Solved)
A small pendulum bob having a mass of 150g is suspended by an inelastic string of length 0.5m. The mass is made to rotate in a horizontal circle of radius 0.4m and whose centre is vertically below the point of suspension
(i) Determine the tension in the string
(ii) State one application of the pendulum
Date posted: April 2, 2019. Answers (1)
- The figure below shows an object of mass 0.2kg whirled in a vertical cycle of radius 0.5m at uniform speed of 5m/s(Solved)
The figure below shows an object of mass 0.2kg whirled in a vertical cycle of radius 0.5m at uniform speed of 5m/s
Determine
(i) The tension in the string at position A
(ii) The tension in the string at position B
(iii) The tension in the string at position C
(iv) From the values obtained in (i) (ii) and (iii) above, determine the point the string will most
likely snap. Explain
Date posted: April 2, 2019. Answers (1)
- Explain why a cyclist going round a bend at high speed tilts inwards(Solved)
Explain why a cyclist going round a bend at high speed tilts inwards
Date posted: April 2, 2019. Answers (1)
- A car of mass 1.5 x 103kg negotiates a level round about of radius 20m at a speed of
10m/s. Calculate the centripetal force acting on...(Solved)
A car of mass 1.5 x 103kg negotiates a level round about of radius 20m at a speed of
10m/s. Calculate the centripetal force acting on the car
Date posted: April 2, 2019. Answers (1)
- A fun fair ride of diameter 12m makes 0.5 revolutions per second.
(Solved)
A fun fair ride of diameter 12m makes 0.5 revolutions per second.
(i) Determine the periodic time, T, of the revolutions.
(ii) Determine its angular velocity.
(iii) Determine the linear velocity of the child riding in it.
(iv) If the mass of the child is 30 kg, find the centripetal force that keeps the child in the
motion.
Date posted: April 2, 2019. Answers (1)
- Give a reason why bodies in circular motion undergo acceleration even when their speed is constant(Solved)
Give a reason why bodies in circular motion undergo acceleration even when their speed is constant
Date posted: April 2, 2019. Answers (1)
- A ship of mass 1300 tonnes floats on sea water:(Solved)
A ship of mass 1300 tonnes floats on sea water:
(i) What volume of sea water is displaced (Density of sea water is 1025kg/m3)
(ii) Suppose it sails from sea water to fresh water, what cargo must be removed so that the same volume of water is displaced? (Density of fresh water = 1000kg/m3
Date posted: April 2, 2019. Answers (1)
- A block of glass of mass 250g floats in mercury. What volume of glass lies under the surface
of Mercury? Density of mercury is 13.6 x...(Solved)
A block of glass of mass 250g floats in mercury. What volume of glass lies under the surface
of Mercury? Density of mercury is 13.6 x 103 Kg/m3.
Date posted: April 2, 2019. Answers (1)
- A gas is put into a container of fixed volume at a constant volume at a pressure of 2.1 x 105.
Nm-2 and temperature 27°C. The...(Solved)
A gas is put into a container of fixed volume at a constant volume at a pressure of 2.1 x 105.
Nm-2 and temperature 27°C. The gas is then heated to a temperature of 327°C. Determine
the new pressure
Date posted: April 2, 2019. Answers (1)