P. 4177. A uniform rod of mass m=0.5 kg and of length =80 cm is hanged with two threads. What will the acceleration of point A and the tension in the left thread be right after cutting the thread on the right? Đáp số: Sức căng dây P. 4198. A small block of mass m=1 kg is placed to a plank which moves on a horizontal frictionless surface, as shown in the figure. The mass of the plank is M=4 kg, and its length is L=0.8 m. The coefficient of friction between the plank and the block is =0.4. a) What is the least constant force F 0 with which the plank must be pulled in order to make the block slide down from it? b) How long does it take for the bock to slide down if the pulling force is F 1 =3 mg? c) Till the instant when the block fell off the plank what percent of the force F 1 increased the internal energy of the system? P. 4237. A path is made to a uniform density cube of mass m, and of edge a, such that when the cube rolls along the path without skiding, its centre moves along a straight line (``square wheel''). At the ``top'' of the path a horizontal initial velocity of v 0 is given to the centre of the cube. The static frictional force is big enough, so the cube do not slide anywhere. What is the speed of the centre of mass when the cube touches the lowest point of the path? (The moment of inertia of the cube with respect to its centre of mass is 2 6 1 ma ) Đáp số: P. 4241. A sample of ideal gas is taken through the cyclic process shown in the figure. a) What is the relation between T 1 , T 2 and T 3 ? b) Express the efficiency of the heat engine which carry out this cyclic process in terms of and . c) In case of air between what values can this efficiency vary? a.) b.) c.) 0< <2/7. Một mẫu của khí lý tưởng được thực hiện thông qua quá trình tuần hoàn được hiển thị trong hình. a) mối quan hệ giữa T1, T2 và T3 là gì? b) Express hiệu quả của động cơ nhiệt trong đó thực hiện quá trình này cyclic về và. c) Trong trường hợp của không khí giữa những gì mà các giá tr P. 4247. As the figure shows, a small object is dropped to a fixed, frictionless slope of angle of elevation =30 o from a height h. The time of the fall is t 1 . After a totally inelastic collision the object slides down the slope. It covers the same distance s=h on the slope during the time t 2 . Determine the ratio of t 1 /t 2 . P. 4243. The number of turns of a solenoid (straight coil) of length L=0,5 m is N=2000, the area of its cross section is A=16 cm 2 , and it has an iron core of relative permittivity of r =2500. At a moment the current in the coil changes at a rate of 100 A/s. What is the induced voltage in that long straight wire of length 2 =20 cm (the wire is next to the centre of the coil) a) which is perpendicular to the axis of the coil, if its two ends are equidistant from the coil, and its centre is at a distance of from the coil? b) which has the same direction as the previous one, and one of its end is at a distance of from the axis of the coil? . in the left thread be right after cutting the thread on the right? Đáp số: Sức căng dây P. 4 198 . A small block of mass m=1 kg is placed to a plank which moves on a horizontal frictionless. air between what values can this efficiency vary? a.) b.) c.) 0< <2/7. Một mẫu của khí lý tưởng được thực hiện thông qua quá trình tuần hoàn được hiển thị trong hình. a) mối quan hệ giữa