Question

8. A body is moving with a speed of 20 m/s. When a certain force is applied, an
acceleration of 4 m/s” is produced. After how much time will its velocity become
80 m/s?
​

Answer 1

Given, A body is moving with a speed of 20 m/s. When a certain force is applied, an acceleration of 4 m/s² is produced.

• To find, After how much time will its velocity become 80 m/s?

Solution :

Initial velocity, u = 20m/s

• Acceleration, a = 4m/s²

Final velocity, v = 80m/s

• Time, t = ?

According to the first equation of motion

→ v = u + at

→ 80 = 20 + 4 × t

→ 80 - 20 = 4t

→ 60 = 4t

→ t = 60/4

→ t = 15 sec

•°• After 15 sec body's velocity will become 80 m/s.

• More to know :

★ Second equation

• s = ut + ½ at²

★ Third equation

• v² = u² + 2as

Answer 2

Given:-

• A body is moving with a speed of 20 m/s. When a certain force is applied, an acceleration of 4 m/s² is produced.

To find:-

• Time taken to become velocity 80 m/s.

Equation Used:-

• ${\boxed{\bf{First\: Equation\:of\:Motion:v=u+at}}}$

Here,

• v = Final Velocity

• u = Initial Velocity

• a = Acceleration

• t = Time taken

Solution:-

Using first equation of motion,

$\sf :\implies\:v=u+at$

Here,

• v = 80 m/s

• u = 20 m/s

• a = 4 m/s²

Putting values,

$\sf :\implies\:80=20+4t$

$\sf :\implies\:4t=80-20$

$\sf :\implies\:4t=60$

$\sf :\implies\:t=\dfrac{60}{4}$

$\sf :\implies\:t=15\:sec$

Hence, It will take 15 sec to become velocity 80 m/s.

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