How to do the second sub question of question 9 on page 89 of the mathematics book of the sixth grade volume I of the people's education press?

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• 13. A 500N object is still on the horizontal ground, and the pressure on the ground is 0______ N. If the object is subjected to 100N vertical upward tension, the pressure on the ground is______ N. If the object is placed on an inclined plane, the pressure on the inclined plane will decrease______ 500N (fill in "greater than", "equal to" or "less than")
• 14. Under the action of horizontal tension f = 100N, the object with weight g = 500N slides along the horizontal ground at a uniform speed 1. If the horizontal pulling force is suddenly removed, find the sliding friction F when the pulling force is removed 2. If the gravity of the object is increased by 100N, in order to keep the object moving in a uniform and straight line, what is the horizontal tension f '?
• 15. There is a 100N object on the rough horizontal ground, which moves forward at a constant speed of 10m in 10s with 20n horizontal tension A. The power of gravity is 100wb. The power of supporting force is 100wc. The power of pulling force is 200wd. The power of pulling force is 20W
• 16. Xiao Zhang uses a horizontal pull force of 30n to lift an object with a weight of 100N and make it move 5m horizontally. After that, the pull force does work J and the gravity does work J The explanation of gravity work,
• 17. When an object weighing 100N is pulled horizontally to the right by 20n and moves horizontally to the right at a constant speed for 5m, the work done by the pulling force is______ J. What does gravity do______ J. What is the resistance to an object______ N. Direction______ ．
• 18. If someone pulls a 100N object forward 5m on the horizontal ground with a 50N horizontal pulling force, the work done by the pulling force on the object is () the work done by gravity on the object ( Big brothers and sisters, help to solve this problem
• 19. When an object moves eastward at a speed of 5 m / s for 6 m / s, and northward at a speed of 3 M / s for 4 S, the velocity of the object in the 10 s is the same What is the average speed.
• 20. The pulley block is used to pull the object a on the horizontal ground to move forward at a uniform speed of 5m within 10s. If the weight of the object is 10000n, the friction between the object and the ground is 200N, the mechanical efficiency of the pulley block is 80%, and the friction of the machine itself is not taken into account. To find out (1) how much work is done by the pulling force? How much extra work is done? (2) how much is the pulling force F? (3) how much is the pulling force power?