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13g of zinc combines with 6,4g of sulphur.

 

a) What is the empirical formula of zinc sulphide?

 

b) What mass of zinc sulphide will be produced?

 

c) What percentage does each of the elements in zinc sulphide contribute to its mass?

 

d) The molar mass of zinc sulphide is found to be `97, 44g*m o l^-1` . Determine the molecular formula of zinc sulphide.

29 August 2015 · Allen maseke · 0 marks · 0 mins

A force of 200 N, acting at `60^circ` to the horizontal, accelerates a block of mass 50 kg along a horizontal plane as shown:

force.png

  1. Calculate the component of the 200 N force that accelerates the block horizontally.
  2. If the acceleration of the block is `1,5 " m" cdot"s"^{−2}`, calculate the magnitude of the frictional force
    on the block.
  3. Calculate the vertical force exerted by the block on the plane.
24 November 2011 · Heather Williams · 0 marks · 0 mins

A student of mass 70 kg investigates the motion of a lift. Use `g=10 quad"m"cdot"s"^{-2}` While he stands in the lift on a bathroom scale (calibrated in newton), he notes three stages of his journey.

  • For 2 s immediately after the lift starts, the scale reads 574 N.
  • For a further 6 s it reads 700 N.
  • For the final 2 s it reads 854 N.

Answer the following questions:

  1. Is the motion of the lift upward or downward? Give a reason for your answer.
  2. Write down the magnitude and the direction of the resultant force acting on the student for each of the stages I, II and III.
  3. Calculate the magnitude of the acceleration of the lift during the first 2s.
24 November 2011 · Heather Williams · 0 marks · 0 mins

A rocket of mass 200 kg has a resultant force of 4000 N upwards on it. Use `g=9,8 quad "m"cdot"s"^{-1}`

  1. What is its acceleration in space, where the rocket is not experiencing any gravitational force?
  2. What is its acceleration on the Earth, where it experiences a gravitational force due to the Earth?
24 November 2011 · Heather Williams · 0 marks · 0 mins

[IEB 2001/11 HG1] - Electric Eels
Electric eels have a series of cells from head to tail. When the cells are activated by a nerve impulse, a potential difference is created from head to tail. A healthy electric eel can produce a potential difference of 600 V.

  1. What is meant by “a potential difference of 600 V”?
  2. How much energy is transferred when an electron is moved through a potential difference of 600 V?
04 May 2012 · Heather Williams · 0 marks · 0 mins

[IEB 2001/11 HG1] - Emf
1. Explain the meaning of each of these two statements:

  1. “The current through the battery is 50 mA.”
  2. “The emf of the battery is 6 V.”

2. A battery tester measures the current supplied when the battery is connected to a resistor of `100 quad Omega`. If the current is less than 50 mA, the battery is “flat” (it needs to be replaced). Calculate the maximum internal resistance of a 6 V battery that will pass the test.

04 May 2012 · Heather Williams · 0 marks · 0 mins

An electron moving horizontally in a TV tube enters a region where there is a uniform magnetic field. This causes the electron to move along the path (shown by the solid line) because the magnetic field exerts a constant force on it. What is the direction of this magnetic field?

tv.png

 

A.

upwards (towards the top of the page)

 

B.

downwards (towards the bottom of the page)

 

C.

into the page

 

D.

out of the page

14 May 2012 · Heather Williams · 0 marks · 0 mins

You find a transformer with 1000 windings on the primary coil and 200 windings on the secondary coil.

  1. What type of transformer is it?
  2. What will be the voltage on the secondary coil if the voltage on the primary coil is 400 V?
14 May 2012 · Heather Williams · 0 marks · 0 mins

Calculate the voltage on the secondary coil of a transformer if the voltage on the primary coil is 22 000 V and the ratio of primary windings to secondary windings is 500:1.

14 May 2012 · Heather Williams · 0 marks · 0 mins

Transformers are useful electrical devices.

  1. What is a transformer?
  2. Draw a sketch of a step-down transformer.
  3. What is the difference between a step-down and step-up transformer?
  4. When would you use a step-up transformer?
14 May 2012 · Heather Williams · 0 marks · 0 mins