A bobsledder pushes her sled across horizontal snow to get it going, then jumps in. After she jumps in, the sled gradually slows to a halt. What forces act on the sled just after she's jumped in?

Question

BlackTom AI · Accepted Answer

Because the sled is sliding on the snow after the bobsledder jumps in, three forces are relevant: the weight (gravity) downward, the normal force upward from the snow, and kinetic friction opposing the sled’s motion.

Relevant concepts:
- Newton’s first and second laws: forces determine acceleration; if the sled is slowing, a net horizontal force opposes its motion.
- Weight (gravity) acts on every mass near Earth’s surface as mg downward.
- The contact from the snow provides a normal force (N) upward; if there is no vertical acceleration, N = total weight.
- When two surfaces slide relative to each other, kinetic (sliding) friction acts opposite the direction of motion; its magnitude is f_k = μ_k N.

Step-by-step reasoning:
1) Identify vertical forces: gravity (W = mg) acts downward on the sled (including the rider once she’s in). The snow exerts an upward normal force N. Because the sled is not accelerating vertically immediately after she jumps in, N − mg = 0, so N = mg.
2) Identify horizontal forces: the push she gave occurred before she jumped in; once she is in and not pushing, there is no continuing applied forward force. The sled is sliding relative to the snow, so the only significant horizontal contact force from the surface is kinetic friction, which acts opposite the velocity and produces the deceleration.
3) Air resistance could also exist, but elementary treatments focus on kinetic friction as the dominant retarding force; typical multiple-choice answers list kinetic friction rather than air drag.

Why this is correct and why other choices are wrong:
- “Gravity and normal only” is incorrect because that would give no horizontal deceleration; the sled would coast at constant speed, contrary to “gradually slows to a halt.”
- “Static friction” is wrong because static friction applies when surfaces do not slide; here the sled is sliding, so kinetic friction applies.
- Any option that includes a continuing applied forward push is wrong because the push ended when she jumped in.

Therefore the forces acting just after she jumps in are gravity, a normal force, and kinetic friction, which matches the provided answer.

A bobsledder pushes her sled across horizontal snow to get it going, then jumps in. After she jumps in, the sled gradually slows to a halt. What forces act on the sled just after she's jumped in?单项选择题

类似问题

A wooden crate is sitting on a factory floor. You push on the crate with a horizontal force that slowly increases from zero. At the exact moment the crate "breaks free" and begins to slide, which of the following is correct?

What is a resistive force?

What is the unit of friction force and what is the unit of coefficient of friction?

What is the difference between friction force and coefficient of friction?

What does a coefficient of friction depend on? What does a coefficient of friction not depend on?

What is the difference between static and kinetic friction forces?

What is the cause of friction between an object and its environment?

Why does an object have the friction force and what is the direction of the force?

更多留学生实用工具

智能学习助手

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