A flywheel on a motor goes from rest to 1000 rpm in 6 sec. The number of revolutions made is nearly equal to
A. 25
B. 50
C. 100
D. 250
Answer: Option B
This Question Belongs to Mechanical Engineering >> Engineering Mechanics
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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
Intial angular velocity , ω₀ = 0 [because flywheel moves from rest ]
final angular velocity, ω = 1000 rpm = 1000/60 rev/sec
Time taken , t = 6 sec
We know, the formula,
ω = ω₀ + αt
Where α is angular acceleration.
1000/60 = 0 + α6
α = 1000/360 = 100/36 = 25/9 rev/s²
Now, use formula
θ = ω₀t + 1/2αt²
= 0 + 1/2 × 25/9 × (6)²
= 1/2 × 25/9 × 36
= 1/2 × 25 × 4
= 50 rev
Ans : v = u + at
1000/60 = 0 + 6a
a = 2.78
S = ut +. 5at^2
= 0 +. 5 * 2.78 * 36
= 50
How to get the answer?