Question

. A truck of mass 1000 kg, increases its speed from
36 km h-1 to 72 km h-1. Find the increase in its
kinetic energy​

Answer 1

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siddhartharao77

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Mass of car m = 1000 kg

velocity = 36 km/h = 36 x 5/18 = 10 m/s

velocity = 72 km/h = 72 x 5/18 = 20 m/s

Initial kinetic energy = ½ mv2

= ½ x 1000 x (10)2

= 50000 J

Increased kinetic energy = 1/2 mv2

= ½ x 1000 x (20)2

= 200000 J

Work done = Change in kinetic energy

= 200000 - 50000

= 150000 J

Answer 2

Given :

• mass of truck, m = 1000 kg
• initial speed of truck, u = 36 km h⁻¹
• final speed of truck, v = 72 km h⁻¹

To find :

• increase in kinetic energy of truck

Knowledge required :

• Formula to calculate Kinetic energy

    $\red{\bigstar}\boxed{\sf{K.E.=\dfrac{1}{2}mv^2}}$

[ where m is mass of object, v is velocity of object ]

Solution :

Converting initial and final velocity given in km h⁻¹ into ms⁻¹

$\longrightarrow\sf{u=36\;kmh^{-1}}$

$\longrightarrow\sf{u=36\times\dfrac{5}{18}\;ms^{-1}}$

$\red{\longrightarrow\sf{u=10\;ms^{-1}}}$

and

$\longrightarrow\sf{v=72\;kmh^{-1}}$

$\longrightarrow\sf{v=72\times\dfrac{5}{18}\;ms^{-1}}$

$\red{\longrightarrow\sf{v=20\;ms^{-1}}}$

Calculating initial Kinetic energy of Truck

$\longrightarrow\sf{Initial\:K.E.=\dfrac{1}{2}mu^2}$

$\longrightarrow\sf{Initial\:K.E.=\dfrac{1}{2}\times (1000)\times(10)^2}$

$\underline{\underline{\red{\longrightarrow\sf{Initial\:K.E.=50,000\;\;J}}}}$

Calculating final Kinetic energy of Truck

$\longrightarrow\sf{final\:K.E.=\dfrac{1}{2}mv^2}$

$\longrightarrow\sf{final\:K.E.=\dfrac{1}{2}\times(1000)\times(20)^2}$

$\underline{\underline{\red{\longrightarrow\sf{final\:K.E.=2,00,000\;\;J}}}}$

Calculating Increase in Kinetic energy

$\longrightarrow\sf{change\:in\:K.E.=(final\:K.E.)-(initial\:K.E.)}$

$\longrightarrow\sf{change\:in\:K.E.=(2,00,000)-(50,000)}$

$\boxed{\underline{\underline{\red{\longrightarrow\sf{change\:in\:K.E.=1,50,000\;\;J=150\;\;kJ}}}}}$

Therefore,

• There will be an increase of 150 kilo Joules in the kinetic energy of Truck.