问题 单项选择题

在平直轨道上,匀速向右行驶的封闭车厢内,悬挂着一个带滴管的盛油容器,滴管口正对车厢地板上的O点,如图所示,当滴管依次滴下三滴油时,设这三滴油都落在车厢的地板上,则下列说法中正确的是()

A.这三滴油依然落在OA之间,而且后一滴比前一滴离O点远些

B.这三滴油依然落在OA之间,而且后一滴比前一滴离O点近些

C.这三滴油依然落在OA之间同一位置上

D.这三滴油依然落在O点上

答案

参考答案:D

解析:一切物体都具有惯性,即一切物体都有保持静止状态或匀速直线运动状态的性质。在平直轨道上,做匀速直线运动的车厢内,由于具有惯性,滴管滴下的三滴油在水平方向,都要保持原来的运动状态,即与汽车同方向速度大小相等的匀速直线运动,所以三滴油落下的位置在悬点的正下方O点上。故选D

单项选择题
单项选择题

Lying in the sun on a rock, the cougar saw Jeb and his son, Tom, before they saw it. Jeb put his bag down quickly and pulled his jacket open with both hands, making himself look big to the cougar. It worked. The cougar hesitated, ready to attack Jeb, but ready to forget the whole thing, too.
Jeb took off his jacket, grasped Tom and held him across his body, making a cross. Now the cougar’s enemy looked even bigger, and it rose up, ready to move away, but unfortunately Tom got scared and struggled free of Jeb.
"Tom, No!" shouted his father.
But Tom broke and ran and that’s the last thing you do with a cougar. The second Tom broke free, Jeb threw himself on the cougar, just as it jumped from the rock. They hit each other in mid air and both fell. The cougar was on Jeb in a flash, forgetting about Tom, which was what Jeb wanted. Cougars are not as big as most people think and a determined man stands a chance, even just with his fists. As the cougar’s claws got into his left shoulder, Jeb swung his fist at its eyes and hit hard. The animal howled (吼叫) and put its head back. Jeb followed up with his other fist. Then out of the comer of his eye, Jeb saw Tom. The boy was running back to help his father.
"Knife, Tom," shouted Jeb.
The boy ran to his father’s bag, while Jeb started shouting as well as hitting, to keep the cougar’s attention away from Tom. Tom got the knife and ran over to Jeb. The cougar was moving its head in and out, trying to find a way through the wall. Jeb was making out of his arms. Tom swung with the knife, into the cougar’s back. It howled horribly and ran off into the mountains.

How did Jeb try to hold the cougar’s attention

A.By keeping shouting and hitting.

B.By making a wall out of his arms.

C.By throwing himself on the cougar.

D.By swinging his fists at the cougar’s eyes.