Answer:

Explanation:
It is given that,
Mass of the grindstone, m = 3 kg
Radius of the grindstone, r = 8 cm = 0.08 m
Initial speed of the grindstone, 
Finally it shuts off, 
Time taken, t = 10 s
Let
is the angular acceleration of the grindstone. Using the formula of rotational kinematics as :



Let
is the number of revolutions of the grindstone after the power is shut off. Now using the third equation of rotational kinematics as :





or

So, the number of revolutions of the grindstone after the power is shut off is 50.
<h2>
After 1 hour they meet.</h2>
Explanation:
Distance between them = 6 miles
Speed of uphill person = 2.5 miles per hour
Speed of downhill person = 3.5 miles per hour
Relative velocity = 2.5 - ( -3.5 ) = 6 miles per hour
We know
Displacement = Velocity x Time
6 = 6 x Time taken
Time taken = 1 hour
After 1 hour they meet.
Answer:
(B) Dark energy does not exist and there is much more matter than current evidence suggests.
Explanation:
The repulsive force which is accelerating expansion of the universe is called as dark energy. Most of matter present in the universe is the dark matter of about eighty five percent.
So, a collapsing universe would not have the dark energy and there is more matter which is not the dark matter. This theory is rejected because expansion of the universe is observable.
Meter - m
Kilometer - km
Hectometer- hm
Dekameter - dam
Decimeter - dm
Centimeter - cm
Millimeter - mm
Micrometer - μm