Question

12. A body moving in a straight line at 72kmph undergoes an acceleration of 4m/s2. Find its speed after 2 seconds.

Answer 1

Given :

▪ Initial speed = 72kmph

▪ Acceleration = 4m/s²

▪ Time interval = 2s

To Find :

▪ Final speed of body after the given interval of time.

Concept :

❇ Here, acceleration has said to be constant throughout the motion, we can easily apply equation of kinematics to solve this question.

❇ First equation of kinematics :

$\bigstar\:\underline{\boxed{\bf{\red{v=u+at}}}}$

• v denotes final speed
• u denotes initial speed
• a denotes acceleration
• t denotes time

Conversion :

↗ 1kmph = 5/18mps

↗ 72kmph = 72×5/18 = 20mps

Calculation :

$\dashrightarrow\tt\:v=u+at\\ \\ \dashrightarrow\tt\:v=20+(4\times 2)\\ \\ \dashrightarrow\tt\:v=20+8\\ \\ \dashrightarrow\underline{\boxed{\bf{\gray{v=28\:ms^{-1}}}}}\:\orange{\bigstar}$

Answer 2

Given ,

A body moving in a straight line at 72kmph undergoes an acceleration of 4m/s² We need to Find its speed after 2 seconds.

So ,

Initial Speed , u = 72 km/h

⇒ u =  72 * (5/18) = 20 m/s

Acceleration , a = 4 m/s²

Time , t = 2 sec

Use 1st equation of motion.

⇒ v = u + at

⇒ v = 20 + 4 * 2

⇒ v = 20 + 8

⇒ v = 28 m/s

So , the Speed after 5 seconds is 28 m/s