Question

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?

Answer 1

Therefore the average thermal power is = 19.61 W

Step-by-step explanation:

Given that the mass of the rock = 20.0 kg

initial velocity (u) = 8.00m/s

Final velocity = 0

Kinetic fiction
`(\mu_k)` = 0.20.

Friction force = Kinetic fiction× weight

=
`\mu_k mg`

Force = mass × acceleration

`\Rightarrow acceleration =(Force)/(mass)`

`=-(\mu_kmg)/(m)`

`=-\mu_kg`

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

v=u+at

Here a
`=-\mu_kg`

`\Rightarrow 0=8+(-\mu_kg)t`

`\Rightarrow 0.20 * 9.8* t=8`

⇒t = 4.08 s

Now,

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

The change of kinetic energy

=
`(1)/(2) mu^2-(1)/(2) mv^2`

`=(1)/(2)* 20* 8 -(1)/(2)* 20* 0`

=80 J

Thermal energy=80 J

Thermal power = Thermal energy per unit time

`=(80)/(4.08)` w

=19.61 W

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