Question

Can anyone explain all the answers?

1. A roller coaster car is on a track that forms a circular loop in the vertical plane.  Roller coaster car is moving with constant speed. If the car is to just maintain contact with track at the top of the loop, what is the normal force acting on this car at the lowest point of track?
   1. mg
   2. 2mg
   3. 3mg
   4. 0
2. Bucket of water is rotated on the rope in vertical plane. If the length of a rope is increased twice, to prevent water from spilling on the top point of trajectory, how should we change the minimum speed of rotation?

1. We should increase speed twice
2. We should decrease speed twice.
3. We should increase speed 2^1/2times.
4. We should decrease speed 2^1/2 times.
5. We should not change speed at all.

3. A coin is sitting on the edge of rotating turntables. Compare two turntables, A and B. They have the same radius (it means coin sits at the same distance from a center), but different surfaces. We measure the maximum frequency of revolutions for which coin does not slide off the turntables. For turntable A this frequency as twice as big as for turntable B. We can conclude that coefficient of static friction between coin and turntable A is:

1. ½ of coefficient between coin and turntable B
2. the same as for turntable B
3. twice as big as coefficient between coin and turntable B
4. 2^1/2greater than one for turntable B.
5. 4 times greater than for turntable B

4. The gravitational force attractive force between two masses, is F. If the masses are moved to half of their initial distance, what is the gravitational attractive force?
   1. F/4
   2. F/2
   3. 2F
   4. 4F
5. Two massive objects are fixed in their positions. The third object of mass m is placed between these two at the point where gravitational force due to two massive objects is equal 0. The third object is displaced  slightly towards one of massive objects. The total gravitational force on the third object is now:

1. Zero
2. Directed in the direction which depends on which out of two massive objects has greater mass.
3. Directed in the direction of displacement of the third object
4. Directed in the direction opposite to displacement of the third object.
5. Directed perpendicular to displacement of the third object.

Answer 1