B. A pot of boiling water represents a system that is completely open.
Explanation:
Mass of the diskshaped grindstone, m = 1.1 kg
Radius of disk, r = 0.09 m
Angular velocity,
Time, t = 42.4 s
We need to find the frictional torque exerted on the grindstone. Torque in the rotational kinematics is given by :
I is moment of inertia of disk,
So, the frictional torque exerted on the grindstone is .
For the first part of the trip:
we have velocity = 960 km/hr and distance = 2250 km
velocity = distance / time
time1 = distance / velocity = 2250 / 960 = 2.34375 hours
For the second part of the trip:
we have velocity = 805 km/hr and distance = 1320 km
velocity = distance / time
time2 = distance / velocity = 1320 / 805 = 1.63975 hours
For the total trip:
we have:
total distance covered = 2250 + 1320 = 3570 km
total time taken = 2.34375 + 1.63975 = 3.9835 hours
average velocity = total distance / total time
average velocity = 3570 / 3.9835 = 896.1968 km/hr
The resistance that one surface or object encounters when moving over another.
"a lubrication system that reduces friction”