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YOUR PARTICIPATION FOR THE GROWTH OF PHYSICS REFERENCE BLOG

Tuesday, December 12, 2017

The first column in the table gives four examples of work being done. The second column gives more detail of the action.



Question 5
The first column in the table gives four examples of work being done. The second column gives more detail of the action.

Which row is not correct?





Note: The question is the same in both papers, except that in the November 2011 one, ‘gravity’ is used instead of ‘gravitational field’ for option A.






Reference: Past Exam Paper – November 2011 Paper 13 Q16 + June 2017 Paper 13 Q14





Solution:
Answer: A.

Work Done = Force × Distance moved in direction of the force

Case A: a girl dives from a diving board into a swimming pool
Direction of force (gravitational) = downwards
Direction of motion = horizontal
Row A is incorrect. So, the solution to the question is A.



Case B: a man pushes a car along a level road
Both the frictional force and the motion are horizontal.



Case C: an electron is accelerated towards a positively charged plate
Direction of force (electric force) = towards positively charged plate
Direction of motion: electron is moving (accelerating) towards the positive charge



Case D: a piston is pushed outwards as a gas expands
Direction of force = on piston (the atmosphere exerts a force on the surface of the piston)
Direction of motion = piston moves outwards


2 comments:

  1. For Question 5 right, I thought the direction of electric force is from positively charged plate to negatively charged plate?

    ReplyDelete
    Replies
    1. the direction of the electric FIELD (not necessarily force) is from +ve to -ve. But remember that the direction of the electric field is that direction of the force on a positive charge.

      Here, we are considering an electron, which is negative. An electron will be attracted to the positive plate. So, the direction of the FORCE is towards the positive plate.

      Delete

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