题干

两个完全相同的金属小球AB带有电量相等的电荷,相隔一定的距离,两球间相互吸引力的大小是F,今让与AB大小相等、相同材料制成的不带电的第三个小球C先后与AB两球接触后移开,这时,AB两球之间的相互作用力的大小为            (  )

A:

B:

C:

D:

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答案(点此获取答案解析)

A

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University Room Regulations

Approved and Prohibited Items

     The following items are approved for use in residential (住宿的) rooms: electric blankets, hair dryers, personal computers, radios, televisions and DVD players. Items that are not allowed in student rooms include: candles, ceiling fans, fireworks, waterbeds, sun lamps and wireless routers. Please note that any prohibited items will be taken away by the Office of Residence Life.

Access to Residential Rooms

     Students are provided with a combination (组合密码) for their room door locks upon check-in. Do not share your room door lock combination with anyone. The Office of Residence Life may change the door lock combination at any time at the expense of the resident if it is found that the student has shared the combination with others. The fee is $25 to change a room combination.

Cooking Policy

     Students living in buildings that have kitchens are only permitted to cook in the kitchen. Students must clean up after cooking. This is not the responsibility of housekeeping staff. Kitchens that are not kept clean may be closed for use. With the exception of using a small microwave oven (微波炉) to heat food, students are not permitted to cook in their rooms.

Pet Policy

    No pets except fish are permitted in student rooms. Students who are found with pets, whether visiting or owned by the student, are subject to an initial fine of $100 and a continuing fine of $50 a day per pet. Students receive written notice when the fine goes into effect. If, one week from the date of written notice, the pet is not removed, the student is referred to the Student Court.

Quiet Hours

     Residential buildings must maintain an atmosphere that supports the academic mission of the University. Minimum quiet hours in all campus residences are 11:00 pm to 8:00 am Sunday through Thursday. Quiet hours on Friday and Saturday nights are 1:00 am to 8:00 am. Students who violate quiet hours are subject to a fine of $25.