Calculate the force of gravity acting on an object that has a mass of 1.3 kg. the object is on earth so use 9.8 m/s^2 as the acceleration due to gravity. force = mass x acceleration

Gravity constantly acts on the apple so it goes faster and faster ... in other words it accelerates.

Ignoring air resistance, its velocity increases by 9.8 meters per second every second. That is two lots of "per second" and is written:

9.8 m/s2

9.8 m/s2 is the acceleration due to gravity near the Earth's surface. Nearly everything in our lives happens near the Earth's surface, so that value gets used a lot, and is written as a little g:

g = 9.8 m/s2

The average value of g is 9.80665 m/s2, but values are different around the world, such as Calcutta at 9.78548, London at 9.81599 and Tokyo at 9.79805.

So most people just use 9.8 m/s2

there are no contact forces mentioned on the list of choices that you've provided.