Newton’s laws of motion：练习题

An object is moving at a constant velocity in a straight line. According to Newton's First Law of Motion, what can be deduced about the forces acting on it?

A book rests at rest on a flat horizontal table. According to Newton's Third Law of Motion, which force is the reaction partner to the downward gravitational pull of the Earth on the book?

A block block X of mass \(2.0\text{ kg}\) is placed on a rough horizontal surface and connected by a light string over a smooth pulley to a hanging block Y of mass \(3.0\text{ kg}\). A constant frictional force of \(4.0\text{ N}\) acts on block X while it is in motion. If the system is released from rest and the acceleration of free fall \(g\) is \(10\text{ m/s}^2\), what is the tension in the string?

A box with a mass of \(4.0\text{ kg}\) is pushed along a horizontal surface. If a constant resultant force of \(12\text{ N}\) acts on the box, what is its acceleration?

A person of mass \(70\text{ kg}\) stands on a weighing scale inside an elevator. Taking \(g = 10\text{ m/s}^2\), what is the reading on the scale when the elevator is moving downwards with a uniform deceleration of \(2.0\text{ m/s}^2\)?

State Newton’s First Law of Motion and describe the motion of an object when the resultant force acting on it is zero.