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Answers
Q.2) (B) 3
Q.3) (D) vacuum
Q.4) 1. speed is a scalar quantity while velocity is a vector quantity
2. speed= distance/time while velocity= displacement/time
3. velocity deals with direction, while speed does not.
Q.5) mass= 1500 Kg.
acceleration = - 1.7 m s^-2
we know that Force= mass * acceleration
so, force= - 2550 N. negative sign indicates that force is acting on opposte direction.
Q.6) Although flash and thunder are produced simultaneously, thunder is heard a few second after the flash is seen, this is because the speed of light in air is more than that of the speed of sound. therefore the flash is seen first and thunder is heard only after.
Q.7) Newton's third law states that for ever action there is an equal and opposite reaction. Yes, this law is also followed by gravitational force.
Q.8) (i) Kinetic energy- energy which a body possesses by virtue of being in motion.
(ii) Potential energy- energy which a body possesses by virtue of being in rest.
(iii) Mechanical energy- mechanical energy is defined as the sum of kinetic and potential energy.
(iv) Gravitation potential energy- energy possessed by the object by virtue of its position in the gravitational field.
(v) Elastic potential energy- potential energy stored as a result of deformation of an elastic object.
(vi) Water energy- water energy is energy derived from the power of water. eg, hydroelectricity.
OR
(i) when the ball is thrown upwards, it reaches a maximum height where velocity= 0 so K.E= 0, at this point P.E will be maximum. when it returns back, the amount of increase in K.E= decrease in P.E
(ii)work done by him=0 because the object kept on his head is perpendicular to the ground. we know
W= F. s. cos ∅, so in this case cos∅= 90 which is 0. hence there'll be no work performed.
Section- B
Q.9) (A) 100° C