问题 计算题

如图所示,皮带的速度是3 m/s,两圆心距离s="4.5" m,现将m="1" kg 的小物体轻放在左轮正上方的皮带上,物体与皮带间的动摩擦因数μ=0.15,电动机带动皮带将物体从左轮运送到右轮正上方时,求:

(1)小物体获得的动能Ek;

(2)这一过程摩擦产生的热量Q;

(3)这一过程电动机消耗的电能E是多少?(g="10" m/s2

答案

(1)4.5J(2)4.5J(3)9J

题目分析:(1)根据牛顿第二定律可得:

即物体可与皮带达共同速度

(2)根据公式 ,所以产生的热量为:

(3)根据能量守恒定律可得:

点评:传送带问题物体运动过程分析是基础.本题第(1)题也可以根据动能定理求解.

完形填空

第二节(共5小题;每小题2分,满分10分)

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

Shoppers who carefully plan their visit to the grocery store can save money on their grocery bills.   71 

Shoppers should visit the grocery store on a full stomach by scheduling their trip immediately after a large meal. If that’s not possible, they should find something healthy to eat while preparing a grocery list.   72  

Although having a list and sticking to it is the most important factor in saving money, shoppers must prepare lists wisely in order to save.   73  Many special buys are announced through the local newspapers, so buying the “grocery issue” is worth the investment(投资). However, it’s important to remember that many newer, more expensive products first offered through coupons may not yield enough savings for shoppers to give up the product they usually buy.

74  Once at the store, the shopper who wants to save money should follow a few more rules. The shopper should not stay longer than necessary, because bills go up each minute the shopper is in the store. So, setting a time limit and a cost limit can hold down the bill.   75   If the grocery list is a short one, some shoppers choose to use the small hand-held basket instead of the roomy grocery cart.

A.A carefully planned list should include in – season produce and any items on sale or discounted through coupons (优惠券).

B.Of course, the shopper should stick strictly to the shopping list and resist the temptation to buy additional items.

C.People who are full are less tired and more likely to buy what they want.

D.Now that the shopper has completed the grocery list, it’s time to leave for the store. E.You should keep your shopping list carefully in case you can exchange it for coupons.

F.Most shoppers are less persuaded to buy extra goods when they are not hungry.

G.Shopping when not hungry, sticking to a grocery list, and following a few simple rules will cut down the grocery bill.

单项选择题