Acceleration down a slope is determined by weight component down the slope which is mgsin(angle), therefore a = gsin(angle). This information is frequently used and therefore you should not hesitate committing into your memory.If the angle is increased to 90' , then it would be just like falling freely where acc. is equal to g.
Some thoughts: Falling freely is often the theme of extreme sports like sky diving ,base jump etc. Before going into such ultimate sports, you would want to try some skiing , snowboarding, sliding in water theme parks, roller coaster etc which gives you an acceleration close to g . You can say its an appetizer before the main course.
