1.2 Motion Under Gravity

When objects are moving vertically upwards or downwards, we can use the acceleration of the earth gravitational field. g = 9.81ms-1

When moving downwards acceleration is in the positive direction, it will be +9.81ms-2 (if ignoring air resistance). Oppositely, is the object is going upwards, acceleration will have a negative acceleration at -9.81ms-2.

Examples:

A ball is hit vertically upwards at 22ms-1. Calculate the height after 2.0s.

x = ?

u = 0ms-1

v = ?

a = -9.81ms-2

t = 2.0s

X = ut + ½ at²

X = 22 × 2 + ½ -9.81² x 2²

X = 24.4m

IMPORTANT - There is not horizontal component, take acceleration as a positive or negative value of g, depending on upwards or downwards motion.