When a car turns off the engine and rushes up a slope, the direction of friction between the slope and the car will change xiexiele

When the car rushes up the slope, the direction of friction is opposite to the direction of motion, and it goes down the slope
If there are other conditions attached, please ask for the explanation

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1. The automobile engine is connected with the rear wheel through the transmission. When the automobile moves forward from standstill, the direction of friction between the front wheel and the rear wheel is () A. The friction of the front wheel is forward, the friction of the rear wheel is backward B. the friction of the front wheel is backward, the friction of the rear wheel is forward C. the friction of the front and rear wheels are backward D. the friction of the front and rear wheels are forward
2. Does static friction do work When a car is subjected to static friction, how does the force do work?
3. Is the friction of the car moving on the horizontal plane sliding friction or static friction?
4. Is the static friction force between the car and the ground equal to the weight of the car itself?
5. The dynamic friction coefficient between the vehicle and the road surface is u, and the radius of a road corner is R (assuming that the maximum static friction is equal to the sliding friction, g = 10 / M / s ∧ 2, q) 1 / assuming that the road surface is level, in order to ensure that the car does not slip when turning, how much speed can the car not exceed If the road surface at the turning point of the highway is designed to be high on the outside and low on the inside, so that the road surface and the horizontal plane form an angle of X, at what speed can the car turn, so that there is no friction between the car and the road surface in the radial direction
6. On the smooth horizontal plane, there is a flat car with a length of 10m and a mass of M = 1kg. There is a small block with a mass of M = 1kg at the left end of the car. The small block is given an initial speed. After a period of time, the block does not fall from the car, and the total speed is 5m / s. The initial speed and dynamic friction factor are calculated
7. On the smooth horizontal plane, a car B with mass m = 2kg is at rest, and there is a linear track with length L = 1m on the upper surface of the car At present, a small block a with mass m = 1kg slides onto the left end of car B at speed v = 5m / s, and the dynamic friction coefficient between block a and the horizontal track of car B is 0.3? The main question is (2) the formula MV = mvm-mv1 ① 1 / 2mV ^ 2 = 1 / 2mvm ^ 2-1 / 2mV ^ 2-umgl ② these two formulas are listed by me, but in the answer, the formula ② is 1 / 2mV ^ 2-umgl = 1 / 2mvm ^ 2 + 1 / 2mV ^ 2, why? What's wrong with my formula?
8. As shown in the figure, there is a flat car with length x = 1m and mass m = 10kg, which is still on a smooth horizontal plane. A small block with mass m = 4kg is placed at one end of the car. The dynamic friction coefficient between the block and the car is μ = 0.25. To make the block move to the other end of the car in 2S, what is the horizontal force F acting on the block? (g = 10m / S2)
9. When a car with mass m and length a moves from one end of the flatbed car with mass m and length B to the other end, what are the displacements of the car and flatbed car
10. The mass is m = 10kg, and the flatbed truck is long enough. On the smooth horizontal plane, a small car is placed at the left end, M = 1kg, and u = 0.2 When the speed of the trolley to the ground is 10m / s, calculate the speed of the trolley
11. Traction and friction? Isn't the traction of a car expressed as the friction between the ground and the car? And the friction is not only determined by the roughness and pressure? Is the heavier the car, the greater the traction? How to understand the relationship between traction and friction? I still don't quite understand, such as the same car. No matter what kind of engine is changed, the initial traction is the same, but the rated power is increased?
12. The direction of friction on the front and rear wheels is () (A) The friction of the front and rear wheels are backward, (b) the friction of the front and rear wheels are forward, (c) the friction of the front wheel is backward and the friction of the rear wheel is forward, (d) the friction of the front wheel is forward and the friction of the rear wheel is backward
13. When a car runs at a constant speed on a straight road, does the goods in the car suffer friction
14. A small ball with mass m is hung on the f end of the spring with stiffness coefficient r, and then the small ball is pulled down with force to make the spring elastic?
15. The period of a spring oscillator which vibrates in the vertical direction is t The period of a spring oscillator vibrating in the vertical direction is t. when the oscillator moves upward from the equilibrium position o, another small ball on the same horizontal line with the equilibrium position o just starts to throw upward at the speed vo. When VO is large, the oscillator and the small ball pass through the equilibrium position at the same time?
16. Spring array o point in B, C between the amplitude of 10 cm, cycle 1 second, how to find the acceleration of the oscillator at B point! The ratio of the acceleration of the oscillator at point B to the acceleration at point P 4cm from point o!
17. If the period of a spring vibration is 4S, the period of the acceleration change of the oscillator is___ The period of velocity change is___ .
18. If the stiffness coefficients of two spring oscillators are K1 and K2, and a mass of M is hung after they are connected, what is the period of the system
19. An object a with mass m is hung under the spring with stiffness coefficient K. now a wooden board B with mass of 1 / 3M is used to hold object a, make a move upward, and finally compress the spring If block B is suddenly removed, the instantaneous acceleration of a is a (g)
20. If a spring is compressed for 4cm, a force of 100N is needed to calculate the stiffness coefficient of the spring. If the spring is compressed for 10cm, what is the elastic potential energy of the spring?