III) Beetle Bailey is pulled on a sled over snow-covered ground. The sled is
pulled by a rope that makes an angle of 
with the horizontal. Beetle
has a mass of 60 kg and the sled has a mass of 5 kg. The coefficients of static
and kinetic friction are 
and 
. Find the frictional
force exerted by the ground on the sled and the acceleration of Beetle and the
sled if the tension on the rope is (a) 120 N (b) 150 N.
(a) (Let's assume that the applied force is pulling the sled from the right.)
In order for the object to move, the applied force must be greater than
. The applied force in the x direction is
. This is 
, so the sled doesn't
move. The acceleration is 
and the frictional force is 91.9
N in the -x direction.
(b) If the tension in the rope is 140 N, then
In order for the object to move, the applied force must be greater than
. The applied force in the x direction is
. This is 
, so the sled
moves.
IV) In problem (III), find the work done by the tension in pulling Beetle and the sled over a distance of 10 m.
For part (a), the sled doesn't move, so 
.
For part (b), 
, and
.