Question

8. A uniform force of 4 N acts on a body of mass
40 kg for a distance of '2' metre. The kinetic
energy acquired by the body is
(A) 800 Joule
(B) 8 Joule
(C) 460 Joule
(D) 320 Joule​

Answer 1

Answer:

Option (B) 8 Joules is correct.

Explanation:

Given,

• Force acting on the body, F = 4 N
• Mass of body, m = 40 kg
• Distance covered, s = 2 m
• Initial velocity of body, u = 0

To find,

• Kinetic energy acquired by the body, K.E. =?

So,

Using expression for Newton's second law

→ F = m a

[ where F is force, m is mass and a is acceleration ]

→ 4 = (40) a

→ a = 4 / 40

→ a = 1/10  m/s²

Now,

Using third equation of motion

→ 2 a s = v² - u²

[ where a is acceleration, s is distance, v is final velocity and u is initial velocity ]

→ 2 (1/10) (2) = v² - (0)²

→ v = √(2/5)  m/s

Further,

Using formula to calculate Kinetic energy

→ K.E. = 1/2 mv²

[ where m is mass, v is velocity and K.E. is kinetic energy ]

→ K.E. = 1/2 (40) (√(2/5))²

→ K.E. = 20 × 2/5

→ K.E. = 8 J

Therefore,

• Kinetic energy acquired by the body will be 8 Joules .

Option (B) is correct.

Answer 2

To Find :

• we have to find the kinetic energy acquired by the body.

Solution :

• Force = 4N
• mass of body = 40 kg
• Distance = 2m
• Uniform velocity (u) = 0

As we know that,

$\boxed{\green{\textbf{Force = Mass × acceleration}}}$

4 = 40 × a

a = 4/40

a = 0.1m/s²

• v² = u² + 2as

v² = 0² + 2 × 0.1 × 2

v² = 0.1 × 4

v² = 0.4

v = √0.4

$\pink{\textrm{ Kinetic energy = 1/2 mv² }}$

= 1/2 × 40 × (√0.4)²

= 20 × 0.4

= 8joule

$\large\dag \large { \red{\underline{\bf{Hence }}}}$

⠀⠀$\orange{\textrm{Kinetic energy of body is 8 joules }}$

• Option (B) is correct✓

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