As shown in the figure, the stacked objects a and B, under the action of constant force of size F, move in a straight line at a constant speed along the horizontal plane, then the correct conclusion in the following is () A. In Figure A and B, the friction force on object a is FB. In Figure A and B, the friction force on object B is FC. In figure a, the friction force on object a is 0, and that on object B is FD. In Figure B, the friction force on object a is f, and that on object B is f

In Figure B, AB moves forward in a straight line at the same time, so there is no trend of relative motion between AB, a is not affected by friction, and ad is wrong. Taking AB as a whole as the research object, it is affected by the friction and tension F of the ground in the horizontal direction, and the two forces are balanced, then f = F. in both cases, the friction of B is equal, and B is correct

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1. The spaceship rises at a constant acceleration of a = G2. Due to the overweight phenomenon, the weight of an object with a mass of 10kg measured by a spring scale is 75n? (earth radius is 6400km, g = 10m / S2)
2. One person stands on the scale, its indication is 500N, another hanging spring scale bottom hangs an object of 300N When the person pushes up the object with a force of 100 N, what is the indication of the spring scale? What is the indication of the scale? When the person pulls down the object with a force of 50 N, what are the indication of the spring scale and the scale? Why?
3. When the object with a mass of 50g is suspended under the spring scale, when the spring scale moves upward with uniform acceleration and linear motion of 1.2m/s2, what is the indication? When the spring scale moves upward with uniform deceleration and linear motion of 1.2m/s2, what is the indication?
4. Use the spring scale to pull an object horizontally to move at a constant speed, the number is 0.6N, and then pull it to do a uniform acceleration movement, the reading is 1.8n, 4, and calculate its mass
5. There is a piece of metal weighing 3.8 n in air with a spring scale Immerse it in the overflow cup filled with water, 50 ml of water flows into the measuring cylinder from the overflow cup, and calculate: (1) the volume of the metal block; (2) the buoyancy of the metal block in the water; (3) the reading of the spring scale when the metal block is in the water; (4) the density of the metal block
6. The metal block m is clamped in a rectangular box with compressed light spring, as shown in the figure. The upper and lower plates of the box are equipped with pressure sensors. The box can move along the vertical track, and the metal block never leaves the upper plate. When the box moves vertically with a = 2.0m/s2 acceleration, the pressure of the upper plate is 6.0N, and the pressure of the lower plate is 6.0N 0 n. (g = 10m / S2) (1) what is the gravity of the metal block? (2) If the indication of the upper roof pressure sensor is 0.4 times that of the lower floor pressure sensor, try to find the acceleration value and direction of the box. (3) to make the indication of the upper roof pressure sensor zero, what is the possible situation of the box moving along the vertical direction?
7. The metal block m is clamped in a rectangular box with compressed light spring, as shown in the figure. The pressure sensors are installed on the top and bottom plates of the box, and the box can move along the vertical track. When the box moves upward with a = 2.0 M / S2 acceleration, the pressure displayed by the sensor on the top plate is 6.0 n, and the pressure displayed by the sensor on the bottom plate is 10.0 n Where can this thing be used in real life? Please give an example
8. The metal block m is clamped in a rectangular box with a compressed light spring. Pressure sensors are installed on the upper and lower roof plates of the box. The box can move along the vertical track. When the box moves vertically at a constant deceleration with an acceleration of 6m / S ^ 2, the pressure displayed by the pressure sensor on the upper roof is 6N, and the pressure displayed by the pressure sensor on the lower floor is 10N, What might the vertical motion of the box look like? When the pressure of the upper roof is exactly equal to zero, Mg-F = ma2, the acceleration A2 = - 10 m / S2 is obtained How did you get that?
9. Distance on the map: 5cm actual distance: 200m scale: distance on the map: 3.6cm actual distance: 1.2mm scale: Distance on the map: 4cm actual distance: scale: 1:3000000 Distance on the map: actual distance: 60km scale: 1:500000
10. But my mother put the money in my hand and said to the woman in a loud voice, "I'm glad he likes reading books!" But my mother put the money in my hand and said to the woman in a loud voice, "I'm glad he likes reading books." It's not you who say that mother is reluctant to give you so much money to buy books When I picked up the poem again, I had to admit that my father was right Mom smiles
11. The object with mass m decelerates and rises h under the action of constant force F in the vertical direction A. The gravitational potential energy increases mghb. The kinetic energy decreases FHC. The mechanical energy increases FHD. The increase of gravitational potential energy is less than the decrease of kinetic energy
12. As shown in the figure, a and B balls are attached to the lower end of the vertical suspension light spring, and their mass ma = 0.1kg and MB = 0.5kg. When the spring is at rest, its elongation is 15cm. If the thin line between a and B is cut, what is the amplitude and maximum acceleration of a ball in simple harmonic motion?
13. As shown in the figure, balls a and B are connected by a light spring with a stiffness coefficient of K1, ball B is suspended at point o with a thin line of length L, ball a is fixed directly below point O, and the distance between O and a is L. at this time, the tension of the rope is F1. Now, the spring between a and B is replaced by a light spring with a stiffness coefficient of K2 to balance the system. At this time, the tension of the rope is F2, and the size relationship between F1 and F2 is () A. F1 ＞ f2b. F1 ＜ F2C. F1 = F2D
14. 5. As shown in the figure: the mass of the wooden frame is m, the stiffness coefficient of the light spring is k, the spring is connected with the ball a, and the balls a and B are explained in detail with thin lines How is it stressed
15. A rope with length of L = 60cm is tied with a small ball, which moves in a circle in the vertical plane. Given the mass of the ball M = 0.5kg, find: (1) try to determine the minimum centripetal force when it reaches the highest point; (2) the minimum speed when the ball reaches the highest point and continues to move in a circle; (3) when the speed of the ball at the highest point is 3m / s, the pull of the rope on the ball. (g = 10m / S2)
16. The two balls a and B have the same mass m and are suspended at o point by two equal length thin wires. Between the two balls is a light spring with stiffness coefficient K When the spring is in the horizontal direction and the angle between the two thin wires is θ, the length of the spring is compressed mgtan (θ / 2) / K, why not 2mgtan (θ / 2) / k
17. There is a spring, pull it with 5N force, the total length is 12cm; if pull it with 10N force, the total length is 14N, find the original length of the spring
18. There is a spring with a length of 10 cm. After pulling it with a force of 5 N, the length becomes 12 cm. If pulling it with a force of 10 N, what is the length of the spring?
19. If a spring is pulled with 5N force, the total length is 12cm; if it is pulled with 10N force, the total length is 14cm, what is the original length of the spring?
20. The length of a spring is 12cm when there is no weight on the lower end, 15cm when there is a 0.6N object on the lower end and the spring is stationary. When there is a 1n weight on the lower end of the spring, the length of the spring is () A. 5 cmB. 17 cmC. 20 cmD. 7 cm