All three choices are correct.
Answer:
The convex lens is shaped so that all light rays that enter it parallel to its axis cross one another at a single point on the opposite side of the lens.
Explanation:
It would increase
because the force is directly proportional to the Value of masses given
Answer:
Only main sequence stars have a well-defined relationship between spectral type and luminosity.
Explanation:
Low-mass stars have much longer lifetimes than high-mass stars.
Answer:
a)
b) 
Explanation:
The net force on the car must produce the centripetal acceleration necessary to make this circle, which is 
. At the top of the circle, the normal force and the weight point downwards (like the centripetal force should), while at the bottom the normal force points upwards (like the centripetal force should) and the weight downwards, so we have (taking the upwards direction as positive):
Which means:
The limit for falling off would be 
, so the minimum speed would be:
