Question

machine does 240 J of work in 40 s. Calculate the power of the machine.
A body of mass 60 kg is moving with the velocity of 50 ms? What would be the change
in kinetic energy if its velocity is halved​

Answer 1

Answer:

1) Work done 240J

Time 40 s

Power = Work/Time = 240/40 = 6 J/s

2) Mass m = 60 kg

velocity = 50 m/s

ke= 1/2 × m× v^2

= 1/2×60×50×50 = 75000 J

Now

velocity halved means new velocity = 25m/s

so, Ke= 1/2×60×25×25 = 18750 J

KE2/ke1= 18750/75000=1/4

{change in KE= (75000-18750)= 56250J}

or, KE1/KE2 = 1/2×60×50×50 / 1/2×60×25×25

KE1/KE2 = 4

New KE is 1/4 th of KE1

Answer 2

Question (1)

Machine does 240 J of work in 40 s. Calculate the power of the Machine.

Solution (1)

Since, Power = work / time

therefore,

→ Power = 240 / 40

→ Power = 6 J/s = 6 Watt

therefore,

• Power of the machine is 6 Watt.

Question (2)

A body of mass 60 kg is moving with the velocity 50 m/s. What would be the change in kinetic energy if its velocity is halved?

Solution (2)

mass of body, m = 60 kg

initial velocity of body, u = 50 m/s

New velocity of body, v = 1/2 ( u ) = 1/2 (50) = 25 m/s

As we know,

K.E. = 1/2 × ( mass ) × (velocity )²

so,

Calculating Change in kinetic energy of body

→ Change in K.E. = 1.2 m v² - 1/2 m u²

→ Change in K.E. = 1/2 (60) (25)² - 1/2 (60) (50)²

→ Change in K.E. = 30 ( (25)² - (50)² )

→ Change in K.E. = 30 ( 625 - 2500 )

→ Change in K.E. = -56250  Joules

therefore,

• The K.E. of body will be decreased by 56250 Joules.