Question 13
An air-conditioning unit is supported by a rigid beam PQ,
as shown.
Which diagram shows the directions of the horizontal and
vertical forces acting on the ends of the beam?
Reference: Past Exam Paper – November 2016 Paper 11 Q16
Solution:
Answer:
B.
Since the air-conditioning
unit is in equilibrium, the resultant force on the system is zero.
The weight of the unit
acts on the beam PQ. Since the beam is inclined the force appears along the
beam, from P to Q.
Breaking down this force
results in a component to the right and a component downwards.
Now, end Q of the beam is
in contact with the wall. From Newton’s 3rd law, the wall would also
exert a (contact) force on the beam at Q. This force is from Q to P (opposite
in direction of the initial force).
Resolving this force gives
a component upwards and a component to the left.
Why does the weight act along the beam? Isn't weight always act downwards?
ReplyDeleteit acts downwards, but since the beam is not vertical but inclined the force is experienced along the beam.
Deletefor example, try to hold a book with your hand vertically up and in another case, with your hand (and arm) up but inclined.
won't you feel the force along your arm?
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ReplyDeleteThanks
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