practice question


QUESTION 2

2.1. A person pushes a lawnmower of mass 15 kg at a constant speed in a straight line over a flat grass surface with a force of 90 N. The force is directed along the handle of the lawnmower. The handle has been set at an angle of 40° to the horizontal. Refer to the diagram below. 
2.1.1 Draw a labelled free-body diagram for the lawnmower.  (4)

2.1.2. Why is it CORRECT to say that the moving lawnmower is in equilibrium?  (1) 
2.1.3. Calculate the magnitude of the frictional force acting between the
lawnmower and the grass  (3) 

The lawnmower is now brought to a stop. 
2.1.4. Calculate the magnitude of the constant force that must be applied through the handle in order to accelerate the lawnmower from rest to 2 m∙s-1 in a time of 3 s. Assume that the frictional force between the lawnmower and grass remains the same as in QUESTION 2.1.3. (6)


2.2. Planet Y has a radius of 6 x 10^5 m. A 10 kg mass weighs 20 N on the surface of planet Y
Calculate the mass of planet Y.  (4)

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grade 12 acid and base questions


QUESTION 7 (Start on a new page.)


7.1 Nitric acid (HNO3), an important acid used in industry, is a strong acid.
7.1.1 Give a reason why nitric acid is classified as a strong acid. (1)
7.1.2 Write down the NAME or FORMULA of the conjugate base of nitric acid. (1)
7.1.3 Calculate the pH of a 0,3 mol∙dm-3 nitric acid solution. (3)
7.2 A laboratory technician wants to determine the percentage purity of magnesium oxide. He dissolves a 4,5 g sample of the magnesium oxide in 100 cm3 hydrochloric acid of concentration 2 mol∙dm-3
.
7.2.1 Calculate the number of moles of hydrochloric acid added to the magnesium oxide. (3)
He then uses the apparatus below to titrate the EXCESS hydrochloric acid in the above solution against a sodium hydroxide solution

7.2.2 Write down the name of apparatus Q in the above diagram. (1)
7.2.3 The following indicators are available for the titration:

Which ONE of the above indicators (A, B or C) is most suitable to indicate the exact endpoint in this titration? Give a reason for the answer. (3)

7.2.4 During the titration, the technician uses distilled water to wash any sodium hydroxide spilled against the sides of the Erlenmeyer flask into the solution.
Give a reason why the addition of distilled water to the Erlenmeyer flask will not influence the results. (1)
7.2.5 At the endpoint of the titration he finds that 21 cm3 of a 0,2 mol dm-3 sodium hydroxide solution has neutralised the EXCESS hydrochloric acid. Calculate the number of moles of hydrochloric acid in excess. (3)
7.2.6 The balanced equation for the reaction between hydrochloric acid and magnesium oxide is:
MgO(s) + 2HCℓ(aq) → MgCℓ2(aq) + 2H2O(ℓ)
Calculate the percentage purity of the magnesium oxide. Assume that only the magnesium oxide in the 4,5 g sample reacted with the acid. (5)
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