# Tutor profile: Jill B.

## Questions

### Subject: Basic Math

This is a question that was asked by a student to his classmates during a quiz contest. 'Think of a number and multiply it by 3. if 4 is subtracted from your answer, you get the same number' What is the number in the student's mind?

Lets assume that the number he is thinking about is x Therefore 3x - 4 = x Bringing x to the left hand side gives 3x - x = 4 This implies 2x = 4 Dividing both sides by 2 gives x = 2 Therefore the number is 2

### Subject: Basic Chemistry

The following are some common mixtures that can be found in a household. 1) kerosene and water 2) rice grains and bean grains 3) groundnut and its peelings 4) common salt dissolved in water 5) water and dirt particles As a form one student who has done the separation of mixtures, describe how you can help your mother to separate the above mixtures.

1) Using a separating funnel - The mixture is poured into the funnel and the tap opened. Water has a higher density and will settle at the bottom and come out first and is collected with a beaker. As soon as all the water comes out, the tap is closed and kerosene remains in the funnel. 2) By handpicking - Bean grains are just picked with the hand and the rice grains are left behind 3) By winnowing - Air is blown into the mixture to carry away the peelings (which is lighter) 4) By evaporation - The solution is boiled for the liquid to evaporate, leaving behind the dissolved salt. The vapour can as well be collected using a condenser to change it back to water 5) By filtration - The dirty water is passed through a filter. As the clean water is collected using a beaker, the dirt particles remain in the filter.

### Subject: Physics

Water has a specific heat capacity of 4200 J/kg/K. This is very high compared to other liquids like alcohol and mercury a) How much heat is required to raise the temperature of 1 kg of water by 1 K? b) State and explain one use of water which is as a result of its high specific heat capacity. c) Hodja's father uses 10 kg of water at a temperature of 317 K for bath. Hodja uses a heater with a power of 500 W to warm his father's water from a temperature of 302 K. (i) How much heat is supplied by the heater every second? (ii) Determine the change in temperature of the water. (iii) Use the formula Q = mass x specific heat capacity x change in temperature to calculate the quantity of heat needed to heat the water. (iv) How long will he use the heater to cause the required change in temperature?

a) 4200 J (A specific heat capacity of 4200 J/kg/K simply means 4200 J of heat is required to raise the temperature of 1 kg of water by 1 K) b) It is used as a coolant for objects like car radiators because it absorbs much heat before becoming hot. c) (i) 500 J (500 W means 500 joules per second) (ii) change in temperature = 317 K - 302 K = 15 K (III) Q = 10 X 4200 X 15 = 630 000 J (iv) If 500 J of heat is supplied every second, to get the duration to supply 630000 J, the energy is divided by 500. That is, t = 630000/500 = 12600 seconds. Dividing by 60 gives 210 minutes. Dividing by 60 again gives 3 and a half hours.

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