Question

calculate the work done required to stop a car of mass 50 kg moving witha velocity of 54 km/h​

Answer 1

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When a object is moving with a constant velocity, it possess K.E

K.E= ${\frac{1}{2}}$ × m × v²

So, in order to bring the object to rest i.e its same magnitude of energy is required so, as the final final energy comes to zero.

v=60km/hr=16.66m/s

So, magnitude of work that needs to be done =

×m×v

2

Hence, work required to stop the car =

2

1

×1500×16.66

2

=208166.7J=208.17kJ

Answer 2

${Solution}$

Given :-

• Mass of a body is 50kg
• Velocity of a body is 54km/hr

To find :-

• Work done by body

Concept to know :-

Here work done by the body is nothing but work done by change in kinetic energy so If we know the formula for kinetic energy if we substitute the value we can get work done by body and here the velocity of body is in km/hr we have to convert into m/s

• 1km/hr = 5/18 m/s
• kinetic energy = 1/2 m(v²-u²)

m = mass of body

v = velocity of a body

SOLUTION:-

54km/hr = 54×5/18 m/s

54km/hr = 15m/s 

PLUGGING THE VALUES IN FORMULA

K.E = 1/2 m(v²-u²)

K.E = 1/2 ×50(0-15×15)

K.E = 25 ×-225

K.E = -5625 J

So, work done by body is -5625J