Question

A 400-kg bear grasping a vertical tree slides down at constant velocity. What is the friction force that acts on the bear?

Answer 1

`f_k=3920sintheta " N"`

Explanation:

400Kg bear slides down at constant velocity

In order to velocity to be constant, the net force must be zero.

Since that constant velocity = zero acceleration

`F_"net"=ma=m(0)=0`

In order to balance the force due to gravity, the frictional force must be of the same magnitude as it.

`F_"net"=F_"xg"-f_k=0`
`f_k=F_"xg"`

You said slide down, there must be an incline.

The horizontal force acting down and parallel to the surface of the incline is:

`f_k=mgsintheta`
[where `theta` is the angle of inclination with repect to `x`-axis.]

`f_k=400(9.8)sintheta`

`f_k=3920sintheta " N"`