What is the name for the narrowing at the muzzle end of a shotgun barrel?

If the wheels lock when braking suddenly the vehicle: a: loses traction b: lose steering wheel ability c: gain speed slightly d: gain steering ability

The mass of the sun is 1.99×1030kg and its distance to the earth is 1.50×1011m. what is the gravitational force of the sun on the earth?

Why do astronauts in the space shuttle weigh less?