Question

Starting from rest, billy goes down a slide (height of 2.5m above ground) and billy’s mass is 35kg. There is friction acting on billy, when he reaches the ground his speed is 3.5 m/s. How much mechanical energy was lost due to friction (give answer in joules)

Answer 1

In order to determune the amount of mechanicak energy lost, consider that the potential energy at the starting point must be equal to the sum of the energy lost due to the friction, plus the kinetic energy on the ground.

Then, you can write:

`U=E_r+K`

the amount of energy lost is energy associated to the friction.

Solve the previou equation for Er, replace the expressions for U and K, and replace the values of the given parameters, as follow:

`\begin{gathered} E_r=U-K=(35kg)(9.8(m)/(s^2))(2.5m)-(1)/(2)(35kg)(3.5(m)/(s))^2 \\ E_r=643.12J \end{gathered}`

Hence, the amoun of the energy lost was approximately 643.12J