"Power" work and mechanical energy PPT download

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"Power" work and mechanical energy PPT download

Part One Content: Basic Knowledge Key Points

Knowledge point 1 Power

1. As shown in the picture, two students moved the same heavy object from the first floor to the third floor, but the time it took was different. Based on the information provided in the picture, determine which of the following statements is correct (C)

A. Student A does more work and faster work

B. Student B does more work and faster work

C. The work is the same. Student A takes less time to do the work and does the work faster.

D. The work done is the same. Student B takes more time to do the work and does it faster.

2. The power of a machine is 150 W, and its meaning is (C)

A. The work done by this machine can only be 150 J

B. This machine does 150 J of work per minute

C. The work done by this machine per second is 150 J

D. The work done by this machine per second is 150 W

3. In order to fight drought and provide disaster relief, a certain village purchased two water pumps, A and B. If the power of pump A is greater than that of pump B, then when they are both working normally, pump A must be more powerful than pump B (D)

A. Doing more work B. Doing less work C. Doing work slowly D. Doing work quickly

Knowledge point 2: Power calculation formula and its application

4. The ratio of the total work of the two machines is 3:2, the ratio of the time is 3:4, then the ratio of the power is 2:1.

5. The ratio of the distances covered by two cars with equal power at constant speed in equal time is 2:1, then (A)

A. The ratio of the traction forces of the two cars is 1:2

B. The ratio of the traction forces of the two cars is 2:1

C. The ratio of the work done by the two cars is 1:2

D. The ratio of the work done by the two cars is 2:1

Power PPT, Part 2: Comprehensive Capability Improvement

6. A worker uses a horizontal thrust of 100 N to push an object weighing 500 N at a constant speed of 0.5 m/s on a level ground, making it move in the horizontal direction. The power of the horizontal thrust is 50 W.

7. In the process of free fall, the object will move faster and faster. An object falls freely from point A and passes through two points B and C one after another. It is known that AB=BC, as shown in the figure. If the power of the object doing work due to gravity in segment AB is P1, and the power doing work due to gravity in segment BC is P2, then P1　<(optional ">""=" or "<")P2.

8. As shown in the figure, it is the newly built Kongli Huaihe River Bridge in Huainan, with a total length of about 5 km. On weekends, Xiaoshun and his family drove across the bridge at a constant speed of 20 m/s. If the output power of the car is always 60 kW, then The traction force is 3000 N, and the work done by crossing the bridge is 1.5×107J.

9. In the physical education test of the high school entrance examination, Li Qiang’s rope skipping score was 180 jumps in 1 minute. His mass is 50 kg, and the height of each jump is about 6 cm. Each time he jumps the rope, he overcomes the gravity and does 30J of work. The average power of the rope skipping is about 90W (g is 10 N/kg).

10. Which of the following statements about power is correct (D)

A. The more work a machine does, the greater its power

B. The more powerful the machine, the more work it does

C. The smaller the power of the machine, the less work it will do.

D. The more powerful the machine, the faster it does work.

Power PPT, the third part: expansion, exploration and breakthrough

17. Assume that the resistance f experienced by a car when driving on a level road is proportional to the square of the speed v, that is, f=kv2, and the output power of the car is P and remains unchanged.

(1) What is the relationship between the traction force F and the resistance f when the car is driving, and the speed of the car is maximum? Briefly describe the reasons;

(2) Try to deduce: the maximum speed of car movement v=∛(P/k).

Solution: (1) It can be seen from the meaning of the question that the output power P of the car is constant. According to P=W/t=Fs/t=Fv, it can be seen that the traction force is inversely proportional to the speed, so as the car speed increases, the traction force continues to decrease; The resultant force F of the traction force and the resistance force = F pull - f. Because the traction force decreases, the resultant force on the car also decreases, and the speed of the car increases slower and slower; when the traction force F of the car is equal to the resistance f, The car speed reaches maximum.

(2) When f=F, it can be obtained according to P=Fv

P=Fv=fv=kv2×v=kv3

Solve to get v=∛(P/k)

Keywords: Free download of PPT courseware for the second volume of eighth-grade physics published by the People's Education Press, power PPT download, work and mechanical energy PPT download, .PPT format;

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Update Time: 2024-11-17

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