Forces, movement, shape and momentum：练习题

Which of the following equations correctly represents the total stopping distance of a vehicle?

A car of mass \(1200\text{ kg}\) is traveling at a constant velocity of \(20\text{ m/s}\). The driver applies the brakes, and the car comes to a complete stop in a time of \(4.0\text{ s}\). Calculate the magnitude of the average braking force acting on the car.

A uniform wooden plank of length \(4.0\text{ m}\) is balanced at its center on a pivot. A weight of \(300\text{ N}\) is placed on the plank at a distance of \(1.5\text{ m}\) from the pivot. At what distance from the pivot must a \(450\text{ N}\) weight be placed on the opposite side to maintain equilibrium?

A wooden block is being pushed to the right along a rough horizontal floor. In which direction does the friction force act on the block?

A constant unbalanced force acts on an object of mass \(0.5\text{ kg}\) for a time of \(2.0\text{ s}\). This force causes the velocity of the object to increase from \(4.0\text{ m/s}\) to \(10.0\text{ m/s}\). Calculate the magnitude of the force.

State Newton's third law and describe the relationship between the magnitude and direction of the action and reaction forces.

A uniform horizontal beam is pivoted at its center. A downward force of \(15\text{ N}\) is applied at a distance of \(40\text{ cm}\) from the pivot point. Calculate the magnitude of the moment of this force in Newton metres (\(\text{Nm}\)).

A light horizontal beam is supported at both ends, A and B, which are \(2.0 \text{ m}\) apart. A \(60 \text{ N}\) weight is placed on the beam at a distance of \(0.5 \text{ m}\) from end A. Calculate the upward support force acting at end B.

An object of mass 5.0 kg is placed on a rough horizontal surface. A horizontal force of 20 N is applied to the object, causing it to accelerate at 2.5 m/s².

a) Calculate the resultant force acting on the object.

b) Determine the magnitude of the friction force acting on the object.

c) If the object is pulled for a distance of 8.0 m, calculate the work done against friction during this displacement.

A light horizontal beam of length \(5.0\text{ m}\) is supported by two vertical wires, X and Y, attached to its ends. A painter of weight \(750\text{ N}\) stands on the beam at a distance of \(2.0\text{ m}\) from wire X. The system is in equilibrium.