Circular Motion and static friction

[MIA6]

1. What is the maximum speed with which a 1050-kg car can round a turn of radius 77 m on a flat road if the coefficient of static friction between tires and road is 0.80? What does the static friction have to do with this problem? Is the centripetal force equal to this friction? WHy?
2. A bucket of mass 2.00kg is whirled in a vertical circle of radius 1.10 m. At the lowest point of its motion the tension in the rope supporting the bucket is 25.0 N. a) Find the speed of the bucket. b) How fast must the bucket move at the top of the circle so that the rope does not go slack? for a), I got Fcp=Ft-Fg, ('t' means tension) but someone said it was Fcp=Ft+Fg. But tension and the gravity acts in opposite direction at the lower point?! for b), someone said Ft=0? why?

Thanks.

 

[G01]

What does the static friction have to do with this problem? Is the centripetal force equal to this friction? WHy?

Yes it is. What other forces could possibly be the centripetal force besides friction? Think of it this way. The car wants to slide out of the curve and move off tangent to it. Static friction holds the car "in place" in that direction. (i.e. at the same radius from the center)

2. A bucket of mass 2.00kg is whirled in a vertical circle of radius 1.10 m. At the lowest point of its motion the tension in the rope supporting the bucket is 25.0 N. a) Find the speed of the bucket. b) How fast must the bucket move at the top of the circle so that the rope does not go slack? for a), I got Fcp=Ft-Fg, ('t' means tension) but someone said it was Fcp=Ft+Fg. But tension and the gravity acts in opposite direction at the lower point?! for b), someone said Ft=0? why?

For part a you are right that Fcp=Ft-Fg. For part b, what will be the the acceleration for which the bucket just makes it around the loop? If you know this, you should be able to find the net force on the bucket, and find the speed of the bucket.

 

[MIA6]

For part b, what will be the the acceleration for which the bucket just makes it around the loop? If you know this, you should be able to find the net force on the bucket, and find the speed of the bucket.

If the bucket has no tension, but only gravity, can it still make a vertical circle? Will it fall down? OH, I think it will not because it still has the net force, or centripetal force.