题干

如图所示,木块置于小车上,在水平拉力F作用下,小车和木块一起以速度v沿水平地面向右做匀速直线运动(不计空气阻力).以下三组力属于平衡力的是(  )

①地面对小车的支持力与木块对小车的压力

②小车对木块的摩擦力与木块受到的水平拉力

③地面对小车的摩擦力与木块对小车的摩擦力.

A:仅①

B:②③

C:仅②

D:①②③

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B

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School activities for kids and teens

     July is a month of fun-filled activities for kids and teens as long as you know where to find them. When you want some fun activities for July, consider these ideas happening in this month.

Secret of the Dragon

Time     Monday, July 1, 2013,

 10:30 am

Cost     Adult: $ 7.40

children (number 15 years): half

Bookings  Phone the booking office:

          3403 2578

Address   Brisbane Botanic Gardens

Note      Secret of the Dragon is a magical story about two children who are taken on a dragon ride to explore the universe.

The Search for Life:

Are We Alone?

Time    Thursday, July 4, 2013,

 2:00 pm

Cost     Adult: $ 14.50

         Children (under 15 years): $ 8.70

Bookings  Phone the booking office:

          3403 7689

Address   Brisbane Botanic Gardens

Note      Are we truly alone in space? Is there any life out there? These are the questions asked in this show.

Magic Class

Time     Friday, July 12, 2013,

         10:00 am

Cost      Free

Bookings  Please call 3403 8470 to book your place.

Address   Centenary Community hub, 171 Dande nong Rd

Note      Would you like to be a magician? Then join David, the magician, to learn about real magic with playing cards, coins, ring ropes and DIY projects and be able to become the life of the party.

Science with Me:

Making your own guitar

Time      Saturday, July 20,

           2013, 3:00 pm

Cost       Free

Bookings   Please phone 3403 1226 to book your place.

Address    10, Egginton Close

Note       Do you want to make a guitar with Katy and her mom? Science with Me is going to be with you. Please remember to bring a piece of wood, a hammer, some rubber bands and some nails with you.