1.In which of the following group of animals, coelom is filled with blood ?
(a) Arthropoda
(b) Annelid
(c) Nematoda os brishet elo (d) Echinodermata
(OS eros
2.A force acts on a body of mass 5kg and changes its velocity from 8 m/s to
12 m/s in 4s, then the magnitude of force is :
(a) 8N
(b) 4N
(c) 5N
(d) 6N
OR
3.The resultant force acting on a body is zero, then
(a) Body is in unequilibrium
(b) Body is in equilibrium
(c) body moves with constant acceleration(d) body moves with retardation
NON
6.
4.Iftwo stones A and B are dropped from a tower, then which one has maximum
kinetic energy?
(a) Lighter stone
(b) Heavier stone
(c) Both have equal
(d) None of these
Answers
1.) (a). Arthropoda
2.) (b.). 5 Newton
3.) (b). Body is in equilibrium
4.) (b.) Heavier stone
2.) We know that rate of change in magnitude is directly propartional to applied ForceInitial momentum = 8*5= 40kgm/s
Final momentum= 12*5= 60kgm/s
then, change in momentum = final momentum - initial momentum = 60-40=20 kgm/s
applied Force= 20/4= 5 newton
4.) If they fall together in a vacuum, they will reach the ground simultaneously, because acceleration due to gravity is the same, which is g, and it is independent of the magnitude of the falling mass. They will have the same velocity though different energies with the 2m having twice the amount of kinetic energy as m as they strike the ground together. (Remember the equation for kinetic energy is KE = 1/2mv^2, so here the smaller mass m(P) will have KE of 1/2mv^2, and larger mass 2m(Q) will have KE of mv^2 algebraically as 1/2•2 becomes 1). In the real world air friction is there which will delay the descent of the lower mass m very slightly relative to the larger mass 2m. So the velocity of the smaller mass when it hits the ground will be slightly less than the larger mass due to slightly more energy loss in counteracting friction due to air in comparison to the larger mass. (The friction experienced by a falling body is not only proportional to the coefficient of friction due to air or any medium it falls through, but also the size, shape of the body, and the surface area exposed to the air. As an example you can compare a small dense metal ball to a feather in your mind, the latter being much larger in size but very light in mass which will take substantially longer time to fall and hit the ground through air, compared to the small metal ball). This is Galileo’s famous experiment that he did from the tower of Pisa to show that both heavy and light mass fall to the ground at the same rate when released at the same time from a height on earth with air-friction eliminated (inside a hollow tube with air extracted out). This was before Newton though paving the way for Newton’s universal theory of gravitation. Using Newton’s famous empiric equation on the force of gravitation which is F = G•M•m/d^2, and his second law of motion (F = ma) we can easily show that the rate of fall or acceleration due to gravity is independent of the magnitude of the falling mass. The force of gravity on the falling body is ma which is its weight (where a is the acceleration due to gravity or g). So ma = mg = G•M•m/d^2. So solving for g will give you the following : g = G•M/d^2. You can see that the falling mass m cancelled out from both sides of the above equation leaving us with that mathematical expression for the acceleration due to gravity : g = G•M/d^2. The value of g is directly proportional to mass of the earth or any other celestial body such as another planet, or the moon, or even a star whose g value we may want to calculate for a falling body towards it, and it is inversely proportional to the square of the distance between the larger mass’s center and the smaller mass. It all beautiful and elegant Newtonian gravitational physics, which is all that you will ever need for all terrestrial speeds, or more accurately non-relativistic gravitational physics. Kaiser T, MD (Life long physics, math, cosmology, and science proponent).
1. a) arthropoda
2. b) 4N
3. b) body is in equilibrium
4. b) heavier stone