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When the wood block with mass of M = 1kg is stationary on the platform with height of H = 1.2m, the dynamic friction coefficient between the wood block and the platform As shown in the figure, the wood block with mass of M = 1kg is still at the height of H = 1.2m Dynamic friction coefficient between wood block and platform on platform μ= 0.2, with horizontal thrust f = 20n, Remove the wood block when it has a displacement of S1 = 3M, and fly out of the platform when it slides again and S2 = 1m, Find the speed of the wooden block when it falls to the ground? ( )
Thrust work: F × s1＝60J
Work done by friction: 0.2 × one × nine point eight × （3＋1）＝7.84J
Landing kinetic energy of wood block: 60-7.84 + 1 × nine point eight × 1.2＝63.92J
Then 63.92 = 0.5mv2
v＝11.3
As shown in the figure, the disc with radius r rotates at a uniform speed around the central axis perpendicular to the disc surface, and a small ball is thrown horizontally along the OB direction at h directly above it. To make the ball touch the disc only once and the falling point is B, calculate the initial speed of the disc and the angular speed w of the rotation of the disc
According to the law of flat throwing, r = v0t, H = 1 / 2 GT ^ 2
V0 = R √ (g / 2H)
The ball drop point is B, and the flight time t of flat throwing must be an integral multiple of the rotation period of the disc
t=nT T=2π/w
w=2πn√ (g/2h) (n=1,2,3,.)
I hope it can help you. If you think it makes sense, you can adopt it
The moment of inertia of a uniform disk with mass m and radius r rotating at angular velocity W around an axis passing through its center and in the plane where the disk surface is located is?
Moment of inertia of disc J = 1 / 2 * Mr ^ 2
It has nothing to do with angular velocity ~ only with mass distribution and rotating shaft~
A disk can rotate around the vertical axis passing through the center o point of the disk and perpendicular to the disk surface. Place a small piece of wood block a on the disk, which makes a uniform circular motion with the disk, as shown in the figure. The following statement is correct about the force on wood block a () A. Block a is subjected to gravity, supporting force and centripetal force B. Wood block a is subjected to gravity, supporting force and static friction, and the direction of friction points to the center of the circle C. Wood block a is subjected to gravity, supporting force and static friction, and the direction of friction is opposite to the direction of wood block movement D. Wood block a is subject to gravity, supporting force and static friction, and the direction of friction is the same as that of wood block movement
According to the stress analysis of block a, block a is affected by gravity, support force and static friction
Gravity is vertically downward and the supporting force is vertically upward. These two forces are equilibrium forces. Because the object tends to slide outward along the radius, the direction of static friction points to the center of the circle, and the static friction provides the centripetal force for the object to make circular motion, so B is correct
Therefore: B
As shown in the figure, a disk can rotate around a vertical axis passing through the center of the disk and perpendicular to the disk surface, and a wood block is placed on the disk. When the disk rotates at a uniform speed, the wood block moves with the disk, then () A. The wood block is subjected to the friction of the disk against it, and the direction is away from the center of the disk B. The wood block is subjected to the friction of the disk against it. The direction points to the center of the disk C. There is no friction between the wood block and the disk because they rotate at a uniform speed D. Because the friction always hinders the movement of the object, the direction of the friction of the wood block by the disk is opposite to the direction of the wood block
According to the force analysis of the wood block, the wood block is affected by gravity, supporting force and friction. The gravity is vertically downward and the supporting force is vertically upward. Both gravity and supporting force are in the vertical direction. These two forces are equilibrium forces,
Only the friction force acts as the centripetal force of the circular motion of the object, so the direction of the friction force should point to the center of the circle, so B is correct and a, C and D are wrong
Therefore: B
Why is sliding friction independent of speed? Isn't tension and friction a pair of equilibrium forces when an object is moving? Then, the tension is equal to the friction. The greater the tension, the faster the object will move, and the greater the friction! isn't it? Please answer with junior high school knowledge! Oh, when an object moves in a straight line at a uniform speed, the tension and friction are a pair of equilibrium forces. The teacher did an experiment. He pulled a wooden block with a spring dynamometer. The first speed is slow, the spring dynamometer is 2n, and the second speed is still 2n. Both times move in a straight line at a uniform speed. Are the two pulling forces the same? If so, why? If not, how does the friction remain the same?
When an object moves in a uniform straight line, the tension and friction are balanced, so they are equal. But to accelerate the speed of the object, it is necessary to increase the tension to accelerate the object. If the tension is always greater than the friction, the object will always accelerate. If the object accelerates for a certain time, it will make the object move in a uniform straight line, then
RELATED INFORMATIONS
- 1. As for friction, the correct one in the following statement is () A. The direction of sliding friction is always opposite to the direction of motion of the object B. Sliding friction always hinders the relative motion between objects C. The magnitude of the friction force must be proportional to the pressure between the contact surfaces D. The direction of friction can be perpendicular to the direction of motion of the object
- 2. Why should the trajectory of the particle with the longest flight time in a magnetic field be tangent to the boundary of the magnetic field
- 3. The wood block with mass m is placed on a smooth horizontal plane, and the bullet with mass m is fired in the horizontal direction at velocity V0 and finally remains in the wood block and moves with the wood block in V A,FL=1/2Mv2 B.Fs=1/2mv2 C.Fs=1/2mv02-1/2(M+m)v2 D.F(L+s)=1/2mv02-1/2mv2 The wood block with mass m is placed on a smooth horizontal plane, and the bullet with mass m is fired in the horizontal direction at velocity V0 and finally remains in the wood block and moves with the wood block in V. It is known that when the bullet is stationary relative to the wood block, the wood block advances L, and the depth of the bullet entering the wood block is s. if the resistance F of the wood block to the bullet is constant, then
- 4. A horizontal disc with radius r rotates at a constant angular velocity W. a person with mass m wants to go from the edge of the disc to the center of the disc. What is the attack of the disc on him? The answer is - 1 / 2MR ^ 2W ^ 2
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- 6. A student is holding a small umbrella in the rain. The radius of the edge of the umbrella is R and higher than the horizontal ground h. When the umbrella rotates at an angular speed W, the umbrella throws out from the edge of the umbrella and forms a circle on the ground. What is the radius of the circle?
- 7. The magnitude of sliding friction is related to the pressure on the contact surface and the roughness of the contact surface The size of sliding friction is related to the pressure on the contact surface and the roughness of the contact surface. Please design a simple experiment to verify that the size of sliding friction is related to the pressure on the contact surface. In addition to long wooden boards, there are iron blocks, aluminum blocks and wood blocks of the same quality. Each block is fixed with a small metal hook for traction, Fixed pulley, spring dynamometer, several thin wires
- 8. Does the dog pull the sled in a uniform circular motion with constant acceleration?
- 9. In uniform circular motion, why the greater the acceleration, the faster the direction of velocity changes. (it is best to use illustration)
- 10. The maximum speed of an automobile with a rated power of 80kW on a straight highway is 20m / s, and the mass of the automobile is 2 × 103kg. If the vehicle moves in a straight line with uniform acceleration from standstill, the acceleration is 2m / S2, and the resistance remains unchanged during the movement, try: (1) What is the constant resistance of the car? (2) How long does it take to move in a straight line with uniform acceleration?
- 11. As shown in Figure 2, a disk rotates at a uniform speed around the vertical axis passing through the center in the horizontal plane, and a small object on the disk is stationary relative to the disk and moves with the disk. The centripetal force on the object is correct in the following statement: a A. The direction of the centripetal force points to the center of the disc B. the direction of the centripetal force is the same as the speed direction of the object C. The centripetal force direction is parallel to the rotating shaft D. the centripetal force direction remains unchanged The disc rotates counterclockwise
- 12. Are the objects on the horizontal conveyor belt subject to friction The conveyor belt is horizontal with an object moving forward at a uniform speed. Is this object subject to friction? If it's moving from rest to uniform speed, is there friction
- 13. Four conditions for friction Is it 1. Objects contact and squeeze each other 2. The contact surface is not smooth 3. Relative motion or relative motion trend between objects 4. There is elasticity between objects
- 14. If the three sides of an obtuse triangle are a + 1, a + 2 and a + 3, the value range of a is __
- 15. There are four line segments with the length of 1.2.3.4 respectively. The probability that any three of them will form a triangle is
- 16. The resultant force of each force on an object moving in a uniform circular motion must be a centripetal force Why is it wrong
- 17. The centripetal force of an object in uniform circular motion is a constant force, right?
- 18. Right triangle area formula
- 19. How to prove the formula of the relationship between the radius of the inscribed circle and the trilateral of a right triangle?
- 20. How to determine the direction of friction in physics?