## The law of the machine

1. The problem statement, all variables and given/known data

A screw jack has a single start thread of pitch 7mm and a operating handle 800mm long.when raising a load of 750kg the effort required on thev end of the handle is 26N.
determine for these operating conditions the following :
(a) the mechanical advantage
(b) the velocity ratio
(c) the efficiency of the machine
(d) the law of the machine

2. Relevant equations
vr = 2 x pie x r/p
effiency of the machine = ma/vr x 100%
law of the machine = E = aw+b

3. The attempt at a solution

(a) mechanical advantage = 750 x 9.81/26N = 282.98

(b) the velocity ratio = 2 x pie x 800mm/7mm = 718.07

(c) the effiency of the machine = 282.98/718.07 x 100% = 39.40%

(d) the law of the machine this is where i am struggling i no the formula is E = aw+b

where a is the velocity ratio and w is the load however what does the b stand for and if i need to caculate this how do i do this please help ......
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 Substitute the values of E,a,w in the law of machines to obtain the value of b (it is a constant).
 so i have transposed correctly i think and have came up with this : b = E-a/w therefore b = 26n - 718.07/750 x 9.81 = 16.60 thanks for the quick reply

## The law of the machine

sorry to reply again as i have misread part (e) in the question

it says if the effort needed to raise a load of 400kg is 17N determine :

the law of the machine.

also should the law of the machine when calculated total 17N

thanks again mark

 Quote by series111 also should the law of the machine when calculated total 17N
I don't understand what you mean by this.

However, you have been provided with two sets of values for E and W. Substitute these in the law of machines, and obtain the values of 'a' and 'b' by solving the system of linear equations that you get.

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