Question

Find the chance in kinetic energy if a body having mass 30 kg descends its speed from 20 m/s to 15 m/s
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Answer 1

Answer :

• The change in kinetic energy possessed by the body, ∆K.E. = 2625 J.

Explanation :

Given :

• Mass of the body, m = 30 kg
• Initial velocity of the body, u = 20 m/s
• Final velocity of the body, v = 15 m/s

To find :

• The change in kinetic energy possessed by the body, ∆K.E. = ?

Knowledge required :

• Formula for Kinetic energy possessed by a body, K.E. = ½mv²

[Where, K.E. = Kinetic energy of the body, m = Mass of the body, v = Velocity of the body]

• Formula for change in kinetic energy of a body, ∆K.E. = K.E.' - K.E.

[Where : ∆K.E. = Change in Kinetic energy possessed by the body, K.E.' = Final kinetic energy possessed by the body, K.E. = Initial Kinetic energy possessed by the body]

Solution :

To find the kinetic energy possessed by the body at 20 m/s :

⠀By using the formula for Kinetic energy possessed by a body and substituting the values in it, we get :

⠀⠀=> K.E. = ½mv²

⠀⠀=> K.E. = ½ × 30 × 20²

⠀⠀=> K.E. = ½ × 30 × 400

⠀⠀=> K.E. = ½ × 12000

⠀⠀=> K.E. = 6000

⠀⠀⠀∴ K.E. = 6000 J

Hence, the kinetic energy possessed by the body at 20 m/s is 6000 J.

To find the kinetic energy possessed by the body at 15 m/s :

⠀By using the formula for Kinetic energy possessed by a body and substituting the values in it, we get :

⠀⠀=> K.E. = ½mv²

⠀⠀=> K.E. = ½ × 30 × 15²

⠀⠀=> K.E. = ½ × 30 × 225

⠀⠀=> K.E. = ½ × 6750

⠀⠀=> K.E. = 3375

⠀⠀⠀∴ K.E. = 3375 J

Hence, the kinetic energy possessed by the body at 15 m/s is 3375 J.

To find the change in kinetic energy possessed by the body :

⠀By using the formula change in kinetic energy possessed by a body and substituting the values in it, we get :

⠀⠀=> ∆K.E. = K.E.' - K.E.

⠀⠀=> ∆K.E. = 3375 - 6000

⠀⠀=> ∆K.E. = -2625

⠀⠀⠀∴ ∆K.E. = -2625 J

Hence the change in kinetic energy possessed by the body is 2625 J(Loss in kinetic energy possessed by the body).

Answer 2

Given :-

• Mass of body = 30 kg
• Initial velocity = 20 m/s
• Final velocity = 15 m/s

To Find :-

• Change in kinetic energy

Solution :-

Change in kinetic energy = ∆K.E.

∆K.E. = ( ½ mv² ) - ( ½ mu² )

• m = 30 kg
• u = 20 m/s
• v = 15 m/s

Substituting the value in formula -

= ( ½ × 30 × 15² ) - ( ½ × 30 × 20² )

= ( 15 × 15 × 15 ) - ( 15 × 20 × 20 )

= 3375 - 6000

= - 2625

Change in kinetic energy = 2625 Joules