题干

用手握住酒瓶,使其瓶口朝上竖直静止在手中,则下列说法正确的是(   )

A:酒瓶能静止在手中,是由于手对酒瓶的握力等于酒瓶的重力

B:酒瓶能静止在手中,是由于手对酒瓶的握力大于酒瓶的重力

C:手握酒瓶的力增大,瓶子所受的摩擦力不变

D:手握酒瓶的力增大,瓶子所受的摩擦力也增大

上一题 下一题 0.0难度 选择题 更新时间:2018-07-27 09:37:30

答案(点此获取答案解析)

C

同类题1

阅读理解

Yellowstone Weather

    Yellowstone National Park is at lofty height. Height. Most of the park is above2,275meters.

    Yellowstone's weather is unpredictable. In summer, it may be warm and sunny with temperatures in the high 70s. At night in any given month, the temperature may drop close to freezing. So it is best to come prepared for cold evenings and mornings,especially if you are camping or hiking. When you leave your campsite,please leave it prepared for possible thundershower and wind.

A sunny warm day may become fiercely stormy with wind, rain, sleet and sometimes snow. Without enough clothing, an easy day hike or boat trip can turn into a battle for survival.

Seasonal Weather Information

Spring

Cold and snow continue into May, although temperatures gradually climb. Early in spring, daytime temperatures average in the 40s and 50s; by late May and June, they may reach the 60s and 70s, Nighttime lows fall below freezing.

Summer

Daytime temperatures are usually in the 70s ,occasionally reaching the 80s in the lower elevations(高度). Nights are cool,temperatures may drop in the 40s and 30s―sometimes even the 20s. July and August tend to be somewhat drier, although afternoon thundershowers are common.

Fall

Weather can be pleasant, although temperatures average 10-2 degrees lower than summer readings, Nighttime lows can fall into teens and lower. Snowstorms increase in frequency as the weeks go by or towards the end of the fall season.

Winter

Temperatures often stay near zero throughout the day, occasionally reaching high in the 20s. Subzero nighttime lows are common. Annual snowfall averages nearly 150 inches in most of the park. At higher places, 200-400 inches of snow have been recorded.