Question

A body of mass 5kg has linear momentum of 20kgm/s If a constant force of 5N acts on it in the direction of its motion for 10s. The change in kinetic energy of the body is

Answer is 450J but I have got 40

Answer 1

concept of kinetic energy

Answer 2

Solution :

Given :

↪Mass = 5 kg

↪ Momentum = 50 kgm/s

↪ Force = 5 N

↪ Time = S

Solution :

P( Momentum ) = m × v

20 kg m/s = 5 kg × v

•°• v = 20 kg m/s ÷ 5 kg

v = 4 m/s

Lets find out velocity after 10 Second !

{ v = u + at }

↪v = u + (f/m)t

↪v2= v1 + ( 5/5 * 10 )

↪v2 = 4 + ( 10 )

↪v2 = 14 m/s

Now, According to the Question!

Change in kinetic of the body = mv²/2 - mv²/2

mv²/2 - mv²/2

↪m/2 ( v2² - v1² )

↪5/2 ( 14²- 4² )

↪5/2 [ ( 4 + 14 ) ( 14 - 4 ) ]

↪5/2 [ ( 18 × 10 ) ]

↪5/2 × 180

↪5 × 90

↪450 joule