Physics
The diagram alongside shows an arrangement of three pulleys A, B and C. The load is marked as L and the effort as E.
(a) Name the pulleys A, B and C.
(b) Mark in the diagram the direction of load (L), effort (E) and tension T1 and T2 in the two strings.
(c) How are the magnitudes of L and E related to the tension T1?
(d) Calculate the mechanical advantage and velocity ratio of the arrangement.
(e) What assumptions have you made in parts (c) and (d)?
Machines
ICSE
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Answer
(a) Pulleys A and B are movable pulleys while pulley C is a fixed pulley.
(b) The direction of load (L), effort (E) and tension T1 and T2 in the two strings are marked in the below diagram:
(c) The relation between magnitudes of L and E to the tension T1 is as follows:
The magnitude of effort E = T1
The magnitude of load L = 22 T1 = 4T1.
(d) The mechanical advantage is 22 = 4 as there are two movable pulleys and we know,
M.A. = 2n where, n is the number of movable pulleys.
The velocity ratio = 22 = 4 as there are two movable pulleys and we know,
V.R. = 2n where, n is the number of movable pulleys.
(e) The assumptions made are:
- The pulleys A and B are weightless
- There is no friction between the bearings of the pulleys or the axle.
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The diagram alongside shows a pulley arrangement.
(a) Name the pulleys A and B.
(b) In the diagram, mark the direction of tension on each strand of string.
(c) What is the purpose of the pulley B?
(d) If the tension is T, deduce the relation between (i) T and E, and (ii) E and L.
(e) What is the velocity ratio of the arrangement?
(f) Assuming that the efficiency of the system is 100%, what is the mechanical advantage?
Draw a diagram of combination of three movable pulleys and one fixed pulley to lift up a load. In the diagram, show the directions of load, effort and tension in each strand. Find:
(i) the mechanical advantage,
(ii) velocity ratio and
(iii) the efficiency of the combination in the ideal situation.