What Forces Are Needed to Move a Sled Up an Inclined Plane?

[DJWise]

Friction up a slope (HELP!)

1. A sled weighing 80N rests ona plane inclines at angle 20 degrees to the horizontal. Between the sled and the plane, the coefficient of static friction is .25 and of kinetic friction is .15. A.) what is the least magnitude of the force F parrallel to the flane that will preven the sled from slipping down the plane? B.) What is the minimum mag. of F that will start the sled moving up the plane? C.) What value of F is required to move the sled up the plane at constant velocity?



2. For a I made friction and weight directed down the slope and the Force directed up the slope. I said that the Force had to be greater than the sum of friction and weight directed down the slope. Am I right in my thinking. I don't know how to tackle b and c. For c i got the same answer because accl would equal zero but it doesn't seem logical.

 

[LowlyPion]

1. A sled weighing 80N rests ona plane inclines at angle 20 degrees to the horizontal. Between the sled and the plane, the coefficient of static friction is .25 and of kinetic friction is .15. A.) what is the least magnitude of the force F parrallel to the flane that will preven the sled from slipping down the plane? B.) What is the minimum mag. of F that will start the sled moving up the plane? C.) What value of F is required to move the sled up the plane at constant velocity?

2. For a I made friction and weight directed down the slope and the Force directed up the slope. I said that the Force had to be greater than the sum of friction and weight directed down the slope. Am I right in my thinking. I don't know how to tackle b and c. For c i got the same answer because accl would equal zero but it doesn't seem logical.

In a) the force you need to supply is in addition to the resistance of friction. (Friction helps hold it.) So actually then the Force 80 N down is paid for with the friction AND the force you supply. It's in b) that you have to over come the friction as well as the weight component down the slope.

Once moving in c) you only have to equal the weight and the kinetic friction resistance to maintain unaccelerated velocity.