Forces and motion：练习题

A car of mass 1200 kg accelerates from rest to 20 m/s in 5 seconds. Assuming the resistive forces acting on the car are constant at 800 N, calculate the engine's driving force.

A block is pulled by a force of 50 N at an angle of 30° to the horizontal. Calculate the horizontal component of this force.

Describe the forces acting on a skydiver when they reach terminal velocity, and explain why their acceleration becomes zero.

A student weighs 600 N on Earth. If the gravitational field strength on the Moon is 1.6 N/kg, calculate the student's mass and their weight on the Moon.

A cyclist travels from point A to point B, which are 12 km apart, at a constant speed of 18 km/h.

(a) Calculate the time, in hours and minutes, it takes for the cyclist to travel from point A to point B.

(b) If the cyclist then immediately cycles back from point B to point A along the same route but takes 50 minutes, calculate the average speed of the cyclist for the return journey in km/h.

(c) What is the overall average speed of the cyclist for the entire journey (A to B and then B to A) in km/h?

A student investigates Newton's Second Law of Motion using a trolley, a string, a pulley, and a set of masses. The trolley is placed on a smooth, horizontal track and connected by a string over a pulley to a hanger with slotted masses. The total mass of the system (trolley + masses on trolley + hanger + masses on hanger) is kept constant by transferring masses from the trolley to the hanger.

(a) Describe the experimental procedure the student should follow to collect data to verify Newton's Second Law, specifically aiming to show that acceleration is directly proportional to the net force applied, assuming constant mass. Include details on how measurements would be taken for force, mass, and acceleration.

(b) Explain how the student would analyze the collected data graphically to demonstrate the relationship between force and acceleration. What type of graph would be expected, and what would its gradient represent?

(c) In a separate experiment, a trolley of mass 1.5 kg is accelerated by a net force of 6.0 N. Calculate the acceleration of the trolley.