Question

Calculate the work done to decrease the speed of a car from 108 km/h to 36 km/h. Given that

mass of car is 900 kg.​

Answer 1

Answer:

360000 joule

Explanation:

Initial velocity (u) = 108 km/h = 30 m/s

Final velocity (v) = 36 km/h = 10 m/s

Mass (m) = 900 kg

Distance travelled (s) = ?

We know,

${v}^{2} = {u}^{2} - 2as \\ or \: \: as = \frac{ {u}^{2} - {v}^{2} }{2} \\ or \: \: as = \frac{ {30}^{2} - {10}^{2} }{2} \\ \: \: = \frac{900 - 100}{2} \\ \\ = \frac{800}{2} = 400$

Work done = Force× Displacement

= (Mass × Acceleration) ×Displacement

= m×a s

= 900 × 400 = 360000 joule

HOPE IT HELPS

Answer 2

Answer:

Explanation:

We have the equation for kinetic energy (K.E) as,

$K.E = \frac{1}{2} mv^{2}$ ...(1)

where

m -  the mass of moving object

v  -  the velocity of the object.

Using equation (1),

Initial K.E   $= \frac{1}{2} mu^{2}$

Final K.E     $= \frac{1}{2} mv^{2}$

The change od decrease in kinetic energy ($\Delta K.E$) will be,

 $\Delta K.E =\frac{1}{2} mv^{2} - \frac{1}{2} mu^{2}$

            $= \frac{1}{2} m(v^{2} - u^{2})$  ...(2)

According to the work-energy theorem,

The work done will be equivalent to the change in kinetic energy of the car.

that is,

Work done =  $\Delta K.E$

Given,

Mass of the car (m) = $900$ kg

Initial speed of the car  (u)      =  $108$ km/h

Final speed of the car  (v)       =  $36$ km/h

Convert km/h into m/s by multiplying the velocity with $\frac{5}{18}$

$u = 108 \times \frac{5}{18}$$= 30 m/s$

$v = 36 \times \frac{5}{18}$ $= 10\ m/s$

Substitutes the values into equation(2).

$\Delta KE = \frac{1}{2}\times900\times( 10^{2} - 30^{2} )$

        $= - 360,000$ J

The negative sign in the answer indicates the decrease in kinetic energy.

So, the amount of work required $= 360,000$  J