Test: Acceleration - Class 9

Acceleration = – 4m/s²; Initial speed, u = 60 m s^-1

Time taken = 5s

Acceleration = change in velocity per unit time

a=v-u/t

v= u + at

v = 60 – 4 x 5 = 40 m/s

Both velocity and acceleration are in the downward direction. Thus, they will be considered negative as they are vectors and the upward direction is positive.

u = 20 m/s, a = -4 m/s², t = 2 s.
v = ?
∵ v = u + at
⇒ v = 20 + (-4) (2)
⇒ v = 20 - 8 = 12 m/s

• When the ball moves upward, the force of gravitation is acting in the opposite direction of the ball that is why in that case acceleration is negative or in other words deceleration takes place.
• But when the ball is moving downwards the force of gravitation is in the same direction of the motion of the ball thus acceleration takes place in this case.

• Distance is a scalar quantity that refers to "how much ground an object has covered" during its motion. 
• Acceleration is a vector quantity that is defined as the rate at which an object changes its velocity.
• Velocity is a vector quantity that refers to the speed of an object in a particular direction.

M.K.S. unit of acceleration = 1 m/s²
C.G.S. unit of acceleration = 1 cm/s²

C.G.S unit of acceleration/ M,K.S unit of acceleration = 1 cm/s² / 1 m/s²
= 1 cm / 100 cm = 1/100 =1:100

Calculating acceleration involves dividing velocity by time or we can say,  dividing the meter per second by the second. i.e. [ m/s² = (m/s) /s ]

If a moving body comes to rest, then its acceleration is negative, as it's velocity becomes zero, therefore the acceleration is also zero.

If the velocity of the body is always changing with a uniform rate (uniform acceleration), then the average velocity is given by

Acceleration is a vector quantity that is defined as the rate at which an object changes its velocity. An object is accelerating if it is changing its velocity.