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1.200. A planet of mass M (^) moves along a circle around the Sun with velocity v = 34.9 km/s (relative to the heliocentric reference frame). Find the period of revolution of this planet around the Sun. 1.201. The Jupiter's period of revolution around the Sun is 12 times that of the Earth. Assuming the planetary orbits to be circular, find: (a) how many times the distance between the Jupiter and the Sun exceeds that between the Earth and the Sun; (b) the velocity and the acceleration of Jupiter in the heliocentric reference frame. 1.202. A planet of mass M (^) moves around the Sun along an ellipse so that its minimum distance from the Sun is equal to r and the maxi- mum distance to R. Making use of Kepler's laws, find its period of revolution around the Sun. 1.203. A small body starts falling onto the Sun from a distance equal to the radius of the Earth's orbit. The initial velocity of the body is equal to zero in the heliocentric reference frame. Making use of Kepler's laws, find how long the body will be falling. 1.204. Suppose we have made a model of the Solar system scaled down in the ratio but of materials of the same mean density as the actual materials of the planets and the Sun. How will the orbital periods of revolution of planetary models change in this case? 1.205. A double star is a system of two stars moving around the centre of inertia of the system due to gravitation. Find the distance between the components of the double star, if its total mass equals M and the period of revolution T. 1.206. Find the potential energy of the gravitational interaction (a) of two mass points of masses mland m2located at a distance r from each other; (b) of a mass point of mass m and a thin uniform rod of mass M and length 1, if they are located along a straight line at a distance a from each other; also find the force of their interaction. 1.207. A planet of mass m moves along an ellipse around the Sun so that its maximum and minimum distances from the Sun are equal to r1and r 2 respectively. Find the angular momentum M of this planet relative to the centre of the Sun. 1.208. Using the conservation laws, demonstrate that the total mechanical energy of a planet of mass m moving around the Sun along an ellipse depends only on its semi-major axis a. Find this energy as a function of a. 1.209. A planet A moves along an elliptical orbit around the Sun. At the moment when it was at the distance r0from the Sun its velo- city 'was equal to voand the angle between the radius vector r0and the velocity vector vowas equal to a. Find the maximum and mini- mum distances that will separate this planet from the Sun during its orbital motion. 1.210. A cosmic body A moves to the Sun with velocity vo(when far from the Sun) and aiming parameter 1 the arm of the vector v
relative to the centre of the Sun (Fig. 1.51). Find the minimum dis- tance by which this body will get to the Sun. 1.211. A particle of mass in is located outside a uniform sphere of mass M at a distance r from its centre. Find: (a) the potential energy of gravitational interaction of the particle and the sphere; (b) the gravitational force which the sphere exerts on the particle. 1.212. Demonstrate that the gravitational force acting on a par- ticle A inside a uniform spherical layer of matter is equal to zero. 1.213. A particle of mass m was transferred from the centre of the base of a uniform hemisphere of mass M and radius R into infinity.
Fig. 1.51.
What work was performed in the process by the gravitational force exerted on the particle by the hemisphere? 1.214. There is a uniform sphere of mass M and radius R. Find the strength G and the potential qo of the gravitational field of this sphere as a function of the distance r from its centre (with r < R and r > R). Draw the approximate plots of the functions G (r) and q(r). 1.215. Inside a uniform sphere of density p there is a spherical cavity whose centre is at a distance 1 from the centre of the sphere. Find the strength G of the gravitational field inside the cavity. 1.216. A uniform sphere has a mass M and radius R. Find the pressure p inside the sphere, caused by gravitational compression, as a function of the distance r from its centre. Evaluate p at the centre of the Earth, assuming it to be a uniform sphere. 1.217. Find the proper potential energy of gravitational interac- tion of matter forming (a) a thin uniform spherical layer of mass m and radius R; (b) a uniform sphere of mass m and radius R (make use of the answer to Problem 1.214). 1.218. Two Earth's satellites move in a common plane along cir- cular orbits. The orbital radius of one satellite r = 7000 km while that of the other satellite is Ar = 70 km less. What time interval separates the periodic approaches of the satellites to each other over the minimum distance? 1.219. Calculate the ratios of the following accelerations: the acceleration zvidue to the gravitational force on the Earth's surface,
Earth's surface. What additional velocity has to be imparted to the spaceship to overcome the gravitational pull? 1.231. At what distance from the centre of the Moon is the point at which the strength of the resultant of the Earth's and Moon's gravitational fields is equal to zero? The Earth's mass is assumed to be 11 = 81 times that of the Moon, and the distance between the cen- tres of these planets n = 60 times greater than the radius of the Earth R. 1.232. What is the minimum work that has to be performed to bring a spaceship of mass m = 2.0.103kg from the surface of the Earth to the Moon? 1.233. Find approximately the third cosmic velocity v3, i.e. the minimum velocity that has to be imparted to a body relative to the Earth's surface to drive it out of the Solar system. The rotation of the Earth about its own axis is to be neglected.
1.5. DYNAMICS OF A SOLID BODY
T= —^1 2 - 10. (1.5c)
T —^ /CO nw 2 2 b
1.234. A thin uniform rod AB (^) of mass m = 1.0 kg moves transla- tionally with acceleration w = 2.0 m/s2due to two antiparallel forces F1and F2(Fig. 1.52). The distance between the points at which these forces are applied is equal to a = (^) 20 cm. Besides, it is known that
1.235. A force F = Ai + Bj is applied to a point whose radius vector relative to the origin of coordinates (^0) is equal to r = ai bj, where a, (^) b, A, B are constants, and i, j are the unit vectors of
(1.5d)
(1.5e)
47
the x and y axes. Find the moment^ N^ and the arm^1 of the force^ F relative to the point 0. 1.236. A force Fl= Aj is applied to a point whose radius vector
vector r2= bj. Both radius vectors are determined relative to the origin of coordinates 0, i and j are the unit vectors of the x and y
dr; Ale—r— A
a
f' Fig. 1.52. Fig. 1.53.
axes, a, b, A, B are constants. Find the arm 1 of the resultant force relative to the point 0. 1.237. Three forces are applied to a square plate as shown in Fig. 1.53. Find the modulus, direction, and the point of application of the resultant force, if this point is taken on the side BC. 1.238. Find the moment of inertia (a) of a thin uniform rod relative to the axis which is perpendicular to the rod and passes through its end, if the mass of the rod is m and its length 1; (b) of a thin uniform rectangular plate relative to the axis passing perpendicular to the plane of the plate through one of its vertices, if the sides of the plate are equal to a and b, and its mass is m. 1.239. Calculate the moment of inertia (a) of a copper uniform disc relative to the symmetry axis perpen- dicular to the plane of the disc, if its thickness is equal to b=2.0^ mm and its radius to R = 100 mm; (b) of a uniform solid cone relative to its symmetry axis, if the mass of the cone is equal to m and the radius of its base to R. 1.240. Demonstrate that in the case of a thin plate of arbitrary shape there is the following relationship between the moments of
tually perpendicular axes passing through one point, with axes 1 and 2 lying in the plane of the plate. Using this relationship, find the moment of inertia of a thin uniform round disc of radius R and mass m relative to the axis coinciding with one of its diameters. 1.241. A uniform disc of radius R = 20 cm has a round cut as shown in Fig. 1.54. The mass of the remaining (shaded) portion of the