Certain force acting on a 20 kg mass changes its velocity from 5 m s-1 to 2 m s-1. Calculate the work done by the force.
Mass of the body = 20 kg
Initial velocity, u = 5 m/s
Final velocity, v = 2 m/s
Kinetic energy is given by the expression,
(i) Kinetic energy when the object was moving with a velocity 5 m/s
(ii) Kinetic energy when the object was moving with a velocity 2 m/s
Work done = change in kinetic energy.
Therefore, work done = (Ek)2 - (Ek)5
= 40 − 250 = −210 J
The negative sign indicates that the force is acting in the direction opposite to the motion of the object.
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Fig. 8.11
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Fig. 8.12
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In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water