Question

From kinematics, correct equation of motion for $S$ is/are :

• A. $S=ut-\frac{1}{2}a{t}^2$
• B. $S=ut+\frac{1}{2}a{t}^2$
• C. Both (a) and (b)
• D. None of these

Answer 1

Answer: (C)

Both (a) and (b)

According to the second equation of motion,

$s=ut+\frac{1}{2}a{t}^2$

where, $s$=displacement

$u$=initial velocity

$t$ = time

$a$=acceleration

(i) If the displacement and acceleration are in the same direction, then,

$s=ut+\frac{1}{2}a{t}^2$

where $a$ is the magnitude of the acceleration

For example, a car linearly accelerating on road.

(ii) If the displacement and acceleration are in the opposite direction, then,

$s=ut-\frac{1}{2}a{t}^2$

where $a$ is the magnitude of the acceleration

For example, a ball thrown vertically upwards in air

Hence, the correct option is C.