The correct answer is - Positive acceleration describes an increase in speed; negative acceleration describes a decrease in speed.
A. cgi... they're usually filmed with a greenscreen and is keyed out in editing. known as chroma keying
The only vertical forces are weight and normal force, and they balance since the surface is horizontal. The horizontal forces are the applied force (uppercase F) in the direction the block slides and the frictional force (lowercase f) in the opposite direction.
Apply Newton's 2nd Law in the horizontal direction:
ΣF = ma
F - f = ma
where f = µmg
F - µmg = ma
F = m(a +µg)
F = (20 kg)(1.4 m/s² + 0.28(9.8 m/s²)
F = 83 N
Comets orbit the sun just like planets do. Except a comet usually has a very elongated orbit. Thanks to the laws of gravity comets obey the same laws. A comets orbit takes it very close to the sun and then far away again.
