A weight of 1000 N can be lifted by an effort of 80 N. If the velocity ratio is 20, the machine is
A. Reversible
B. Non-reversible
C. Ideal
D. None of these
Answer: Option A
Solution (By Examveda Team)
Understanding the Question:Imagine a simple machine like a pulley system. It helps you lift heavy objects with less effort.
We have a weight (load) of 1000 N that needs to be lifted.
We only need to apply an effort of 80 N to lift it.
The velocity ratio (VR) is 20. This tells us how much the machine multiplies the effort. A VR of 20 means the effort moves 20 times the distance the load moves.
Mechanical Advantage (MA):
The machine's mechanical advantage (MA) shows how much it multiplies the effort.
We calculate MA by dividing the load by the effort: MA = Load / Effort = 1000 N / 80 N = 12.5
Efficiency:
Efficiency tells us how effective the machine is. It's the ratio of MA to VR:
Efficiency = (MA / VR) * 100% = (12.5 / 20) * 100% = 62.5%
Reversible vs. Non-reversible Machines:
A reversible machine has an efficiency greater than 50%. It can work in the reverse direction without extra help. For example, it can both lift a weight and lower it smoothly.
A non-reversible machine has an efficiency less than 50%. To reverse it (lower the weight), you might need to apply an external force.
Answer:
Since the efficiency (62.5%) is greater than 50%, the machine is reversible. The correct option is A.
This Question Belongs to Mechanical Engineering >> Engineering Mechanics
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Comments (7)
The resultant of two equal forces P making an angle $$\theta ,$$ is given by
A. $$2{\text{P}}\sin \frac{\theta }{2}$$
B. $$2{\text{P}}\cos \frac{\theta }{2}$$
C. $$2{\text{P}}\tan \frac{\theta }{2}$$
D. $$2{\text{P}}\cot \frac{\theta }{2}$$
A. Equal to
B. Less than
C. Greater than
D. None of these
If a number of forces are acting at a point, their resultant is given by
A. $${\left( {\sum {\text{V}} } \right)^2} + {\left( {\sum {\text{H}} } \right)^2}$$
B. $$\sqrt {{{\left( {\sum {\text{V}} } \right)}^2} + {{\left( {\sum {\text{H}} } \right)}^2}} $$
C. $${\left( {\sum {\text{V}} } \right)^2} + {\left( {\sum {\text{H}} } \right)^2} + 2\left( {\sum {\text{V}} } \right)\left( {\sum {\text{H}} } \right)$$
D. $$\sqrt {{{\left( {\sum {\text{V}} } \right)}^2} + {{\left( {\sum {\text{H}} } \right)}^2} + 2\left( {\sum {\text{V}} } \right)\left( {\sum {\text{H}} } \right)} $$
A. $${\text{a}} = \frac{\alpha }{{\text{r}}}$$
B. $${\text{a}} = \alpha {\text{r}}$$
C. $${\text{a}} = \frac{{\text{r}}}{\alpha }$$
D. None of these
MA=1000/80=12.5
VR=20
Efficiency=Ma/VR=12.5/20*100=62.5%
i.e more than 58%,so this machine is reversible machine.
Thank you.
Efficiency=MA/VR
MA(Mechanical Advantage)=W/P
W=1000, P=80, VR=20
If Efficiency is equal to MA and VA then Machine is ideal
Efficiency is greater than 50% then Machine is Reversible
Efficiency is less than 50% then Machine is non reversible or self locking machine
W= 1000N P=80N V.R= 20
WE KNOW, EFFICENCY= M.A / V.R
M.A= W/P = 1000/80= 12.5
EFFICENCY= 12.5/20= 0.625 = 62.5%
M.a- load lift to efforts applied 1000/80=12.5
12.5/20×100= 62.5>50 reversible
Reversible machine : A machine which is capable of doing work in the reverse direction even after the removal of effort ,load get lifted is called Reversible machine.
Non - Reversible machine : A machine which is not capable of doing work in the reverse direction is called Non - Reversible machine. {It is also called self- locking machine} {For non-reversible machine efficiency will be less than 50%}
The term ideal machine refers to a hypothetical mechanical system in which energy and power are not lost or dissipated through friction, deformation, wear, or other inefficiencies.
Efficiency =Mechanical advantage /velocity ratio
=12.5/20 *100= 62.5 >50 %
how?