A car weighing 12 kN has speed of 20 ms⁻¹ . Find its kinetic energy. Ans. (240 kJ)


Given:  

Weight of the car = W = mg =  12 kN = 12ｘ 10³ N
Speed of the car = v = 20 m s⁻¹
gravitational acceleration = g = 10 m s⁻²

To Find:
Kinetic Energy = K.E. = ? 

Solution:   

We have the formula for Potential Energy as

K.E.  = `\frac {1}{2}`mv²

to find mass we are given that

w = m g

or 

m = `\frac {w}{g}`

by putting values 

m = `\frac {12ｘ 10³ N}{10 m s⁻²}`

m = 1.2ｘ 10³ kg

Now using the formula for K.E

K.E.  = `\frac {1}{2}`mv²

by putting values 

K.E.  = `\frac {1}{2}` ｘ (1.2ｘ 10³) kg ｘ (20 ms⁻¹)²

K.E.  = 240ｘ 10³ J

or

K.E.  = 240 kJ

So, the Kinetic Energy of the car is 240 kJ

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