A small metal block with mass of 140 g sits on a horizontally rotating turntable. The turntable makes exactly 2 revolutions each second. The disk is located 6 cm from the axis of ration of the turntable. Answer each of the following question:

a. What is the frictional force acting on the disk?
b. The disk will slide off the turntable If it is located at a radius larger than 11 cm from the axis of rotation. What is the coefficient of static friction?

a) Frictional force acting on the disc = 1.326N

b) Coefficient of static friction = 1.77

Explanation:

mass of the metal block = 140 g = 0.14 kg

Frequency of the turn table = 2 Revs/sec

distance of the disc from the axis of the turn table, r = 6 cm = 0.06 m

a) Frictional force acting on the disc

F = ma

a = V²/r ; V = ωr;

a = ω²r²/r    ;   a = ω²r

F = mω²r

ω = 2πf = 2π * 2 = 4π

ω =  4π

F = 0.14 * (4π)² * 0.06

F = 1.326 N

b) Coefficient of static friction

F = μmg(1)

F = mω²r(2)

Equating (1) and (2)

μmg =  mω²r

μ = ω²r/g

r = 11 cm = 0.11 m

g = 9.8 m/s²

μ = ( 4π)²  *  0.11/9.8

μ = 1.77

carbon is found in all living things. carbon atoms move constantly through

living organisms, the oceans, the atmosphere, and the earth’s crust in what is

known as the carbon cycle. the directions taken by carbon atoms through this

cycle are very complicated and can take millions of years to make a full circle.

all animals, from humans to the dinosaurs are part of the carbon cycle. when

animals eat food, they get carbon in the form of carbohydrates and proteins.

in animals, oxygen combines with food in the cells to produce energy for daily

activity and then gives off carbon. the carbon combines with oxygen to form

carbon dioxide (co2) and is released back into the atmosphere as a waste

product when animals breathe and exhale.

from 145-65 million years ago, earth was much

hotter than today and covered with dense,

tropical swamp forests. the trees and other

plants were immense and

provided an endless supply of

food for the giant animals that

roamed the land. somewhere in

the air above one of these

forests, a lone carbon atom has joined

up with two oxygen atoms to form a molecule of co2.

the co2 molecule was sucked into the tiny holes (stomata) on the leaf of a

fern plant and joined with sunlight, chlorophyll and water to make food and

energy in the plant’s cells through photosynthesis. the oxygen (o2) from the

co2 molecule was sent back into the atmosphere; the carbon atom (c) was

detached and used to make a molecule of sugar.

if that carbon atom had been eaten instead, a totally

different situation would have developed. let’s say

that a giant plant-eating dinosaur (herbivore) ate the

fern for breakfast, and swallowed the carbon in the

fern in the form of carbohydrates and proteins. in

the process of respiration, oxygen combined with

the carbohydrates and proteins in the dinosaur’s cells

to provide energy for its daily activity.  

does anyone know or what?