A jogger is exercising along a long, straight road that runs north-south. She starts out heading north. In what direction is she running at time t = 20 min?

Question

BlackTom AI · Accepted Answer

To determine the jogger’s direction at t = 20 min, we need to look at the velocity versus time graph and identify the sign of the velocity at that exact moment.

Option 1: north. This would be correct if the velocity v_x were positive (pointing in the north direction) at t = 20 min. However, the graph shows a sharp drop in velocity at t = 20 min, changing from a positive value to a negative value right at that point, so the velocity is not positive at t = 20 min. Therefore, this choice misreads the sign of the velocity near t = 20.

Option 2: south. The key to this option is recognizing the discontinuity at t = 20 min: immediately after t = 20, the velocity becomes negative (v_x < 0), indicating motion toward the south. Since the question asks for the direction exactly at t = 20 min, many textbook conventions take the instantaneous velocity at a discontinuity to be the value after the discontinuity for motion direction. In this graph, the velocity right at and just after t = 20 min is negative, corresponding to south.

Option 3: south and then north. This would imply the jogger changes direction within a small interval around t = 20 min, i.e., the velocity would switch signs more than once near t = 20. The provided graph shows a single abrupt change in velocity sign at t = 20, not a back-and-forth pattern, so this option describes a more complex motion than is present.

Option 4: north and then south. This would require the jogger to start moving north, reverse to south, all around t = 20 in a manner that would yield a positive velocity before 20 and a negative velocity after 20 with a defined reversal at or near t = 20. The graph does not show a reversal before 20; it shows a continuous positive velocity up to the moment of the discontinuity, then a jump to a negative value at t = 20, so this option mischaracterizes the motion history.

In summary, the velocity is positive (northward) up to t = 20 min, but at t = 20 min there is an abrupt change to a negative velocity (southward). Since the question asks for the direction at t = 20 min, the negative velocity indicates the jogger is running south at that instant. The correct interpretation aligns with the negative velocity after the discontinuity, which makes south the intended direction at t = 20 min.

SPHY001 Graded Quiz 1 (Unit 1 and Unit 2)- Requires Respondus LockDown Browser

A jogger is exercising along a long, straight road that runs north-south. She starts out heading north. In what direction is she running at time t = 20 min?

查看解析

登录即可查看完整答案

类似问题

An automobile of mass 2000 kg moving at 20 m/s is braked suddenly with a constant braking force of 10,000 N. How far does the car travel before stopping?

What is the meaning of subscript i in vi and subscript f in vf?

What is the difference between average and instantaneous velocity?

What is the difference between velocity and acceleration?

What is a motion?

Joe and Bill throw identical balls vertically upward. Joe throws his ball with an initial speed of twice as high as Bill's ball. The maximum height of Joe's ball will be

Which of the following equations of motion would be used to calculate the displacement given the initial and final velocities as well as the acceleration?

更多留学生实用工具

考试浏览器助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单