Question

Calculate the work done by the engine of a bus of mass 300 kg when it
changes its constant speed from 50 m/s to 80 m/s in 3s.

Answer 1

$\maltese \: \red{\mid{\underline{\overline{\textbf{Answer}}}\mid}}$

It is given that :-

• Mass of engine = 300kg
• Initial velocity = 50m/s
• Final velocity = 80m/s
• Time = 3s.

Now the acceleration of body will be :-

$\maltese \: \frac{v - u}{t}$

After inputting the values we get :

$\maltese \frac{80 - 50}{ 3} = \frac{30}{3} = \cancel \frac{30}{3}$

Acceleration = 10m/s.

Now by third equation of motion :

${v}^{2} = {u}^{2} + 2as$

We have :-

$s = \frac{ {v}^{2} - {u}^{2} }{2a}$

Now after inputting the values we get :

$s = \frac{ {80}^{2} - {50}^{2} }{2 \times 10}$

$s = \frac{6400 - 2500}{20}$

$s = \frac{3900}{20} = 195m$

Therefore the displacement of bus is 195m.

Now work done by engine of bus will be :

$w = force \times displ.$

$w = m \times a \times s$

$w = 300 \times 10 \times 195 = 585000j$

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BY SCIVIBHANSHU

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