Question

A body of mass 500 g is moving with a speed 10 m/s. A force acts on it which makes it to move with a
speed 20 m/s. Find : (1) the change in kinetic energy of the body, and (ii) the work done by the force on the
body.

Answer 1

m=500g=0.5kg

u=10m/s

v=20m/s

(i)Change in Kinetic Energy=1/2mv²-1/2mu²

=1/2m(v²-u²)

=1/2×0.5(20²-10²)

=1/2×0.5[(20+10)(20-10)]

=1/2×0.5×30×10

=1/2×0.5×300

=75j

(ii)According to Work Energy Theorem,

Work done =Change in Kinetic Energy

=>Work Done=75j

Hope it is helpful.

Answer 2

Answers are - (1) 75 J (2) 75 J

Given - Mass and speed

Find - Change in kinetic energy and work done

Solution - Kinetic energy = 1/2*mass*change in velocity²

Change in velocity = final velocity² - initial velocity²

Converting mass in grams to kilograms.

1000 gram = 1 kg

500 gram = 1*500/1000

Mass = 0.5 kg

Keep the values in formula

Kinetic energy = $\frac{1}{2} \times 0.5 \times ( {20}^{2} - {10}^{2} )$

Kinetic energy = $\frac{1}{2} \times 0.5 \times (400 - 100)$

Kinetic energy = $\frac{1}{2} \times 0.5 \times 300$

(1) Kinetic energy = 75 Joules

(2) As per the Work energy principle, the change in kinetic energy is equal to work done. Hence, work done is 75 J.

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