A 20.0 kg rock is sliding on a rough , horizontal surface at8.00 m/s and eventually stops due to friction .The coefficient ofkinetic fricction between the rock and the surface is 0.20
what average thermal power is produced as the rock stops?

Therefore the average thermal power is = 19.61 W

Explanation:

Given that the mass of the rock = 20.0 kg

initial velocity (u) = 8.00m/s

Final velocity = 0

Kinetic fiction = 0.20.

Friction force = Kinetic fiction× weight

                      =

Force = mass × acceleration

To find the time , we use the the following formula,

v=u+at

Here a

⇒t = 4.08 s

Now,

Thermal energy= work done by friction = change of kinetic energy

The change of kinetic energy

=

=80 J

Thermal energy=80 J

Thermal power = Thermal energy per unit time

                          w

                         =19.61 W

Therefore 19.61 W average thermal power is produced as the rock stops.

there is no correct list among the choices you've provided.

the list might look something like this:

-- baby human

-- piccolo

-- flute

-- soprano singer

-- trumpet

-- tenor singer

-- trombone

-- baritone singer

-- baritone horn

-- bass singer

-- tuba

since i had to make up the list myself, i made it easy on myself, and i didn't try to shuffle the string instruments and woodwinds into it too.

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s