Question

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Answer 1

Answer:

Kinetic energy of the ball when it's half way down is 1000 J.

Explanation:

➢Given:

• Mass of the object (m) = 40 kg
• Height (h) = 5 m

➢To find:

Kinetic energy.

➢Solution:

We know that,

Potential energy (P.E.) = mgh

(where m is mass, g is gravity and h is height.)

⇒ P.E. = 40 × 10 × 5

= 2000 J

The object is allowed to fall that means its potential energy will get converted into kinetic energy. So whatever the potential energy is, it should be equal to the kinetic energy.

That means in this condition, P.E. = K.E.

Kinetic energy when its half way down.

2000/2 = 1000 J.

Therefore K.E. = 1000 J.

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Answer 2

We have,

Mass of object = 40 kg

Height (max.) = 5 m

We know,

PE = mgh

Let, g = 10 m/s².

PE = (40 kg)(10 m/s²)(5 m)

⇒ PE = 2000 J

We know, KE = ½ mv² and

v² = 2gh

∴ KE (at middle) = ½ m(2gh) = mgh = (40 kg)(10 m/s²)(2.5 m) = 40 × 25 J = 1000 J = 1 kJ (answer)

ALITER:-

We got that, PE at the highest point = 2 kJ

And, at the halfway down, KE = PE. And they are half the PE at the highest point, according to the law of conservation of energy.

∴ KE = 2 kJ/2 = 1 kJ (answer).