What is the efficiency of a simple screw jack having velocity ratio is 314.2 and mechanical advantage is 220?
Answers
Answer:
The velocity ratio is the length of the circle formed by the tommy bar over the pitch:
\text{V.R.}=\frac{2\pi R}{p}=\frac{2\cdot3.14 \cdot0.4}{0.002}=1256.637.V.R.=p2πR=0.0022⋅3.14⋅0.4=1256.637.
(ii) The mechanical advantage:
\text{M.A.}=\eta\text{V.R.}=0.6\cdot1256.637=753.982.M.A.=ηV.R.=0.6⋅1256.637=753.982.
(iii) The effort required is:
E=\frac{\text{load}}{\text{M.A.}}=\frac{mg}{\text{M.A.}}=\frac{900\cdot10}{753.982}=11.94\text{ N}.E=M.A.load=M.A.mg=753.982900⋅10=11.94 N.
(iv) Work done by the effort. Keep in mind that here we should include the loss of efficiency, or we should only lift the car for 20 cm, but also apply additional effort to overcome friction and other factor included in the efficiency of 60%:
W=\frac{\text{work to lift the car}}{\eta}=\frac{mgh}{\eta}=3000\text{ J}.W=ηwork to lift the car=ηmgh=3000 J.
Answer:
0.7
Explanation:
220/314.2 = 0.7