Name: Lever: Principle of Moments and Mechanical Advantage
Uploaded: 2019-07-19
Duration: 6 min 29 s
Description: Engineers use a lever to magnify the force applied to an object. On what principle a lever works, and how to calculate the mechanical advantage of a lever? L...

Question

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 directions of load (

L

), effort (

E

) and tension

T_{1}

and

T_{2}

in the two strings.
(c) How are the magnitudes of

L

and

E

related to the tension

T_{1}

?
(d) Calculate the mechanical advantage and velocity ratio of the arrangement.
(e) What assumptions have you made in parts (c) and (d)?

Accepted Answer

(a) Pulley A and pulley B are movable pulleys. Pulley C is a fixed pulley.
(b) The direction of load ( $L$ ), effort ( $E$ ) and tension $T_{1}$ and $T_{1}$ in the two strings are marked in the below diagram:

(c) The relation between magnitudes of $L$ and $L$ to the tension $E$ is as follows:
The magnitude of effort, $E = T_{1}$ .
The magnitude of load, $L = 2^{2} T_{1} = 4 T_{1}$ .
(d) The mechanical advantage is $4$ as there are two movable pulleys and we know that,
$M . A = 2^{n}$ , where n is the number of movable pulleys.
The velocity ratio is equal to $4$ as there are two movable pulleys and we know that,
$V . R = 2^{n}$ where, n is the number of movable pulleys.
(e) The assumptions we can made from (c) and (d) are that the pulleys A and B are weightless and there is no friction between the bearings of the pulleys or the axle.

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