Motion and Forces：練習題

The diagram shows a block being pulled by two forces in opposite directions. Force \( P \) is \( 10 \text{ N} \) to the right and Force \( Q \) is \( 3 \text{ N} \) to the left. What is the resultant force acting on the block?

In Motion and Forces, the weight of an object is the force exerted on it by gravity. If an object has a mass of \( 10 \text{ kg} \) and the gravitational field strength is approximately \( 9.8 \text{ N/kg} \), what is its weight?

A car travels a distance of \( 150 \text{ km} \) at a constant speed of \( 50 \text{ km/h} \). How long does the journey take?

A bicycle is traveling at a constant velocity of \( 5 \text{ m/s} \). What is the net force acting on the bicycle?

A car travels from point A to point B. If the distance between the points is \( 120 \text{ km} \) and the journey takes \( 2 \text{ hours} \), what is the average speed of the car?

A car is traveling at a constant speed of \( 15 \text{ m/s} \). If the driver applies a constant braking force that results in a uniform deceleration of \( 3 \text{ m/s}^2 \), calculate the time it takes for the car to come to a complete stop.

A student investigates Motion and Forces by pulling a wooden block of mass \( 2 \text{ kg} \) along a horizontal table using a spring balance.

(a) If the spring balance shows a reading of \( 6 \text{ N} \) while the block is moving at a constant velocity, what is the magnitude of the frictional force acting on the block? Explain your answer. (2 marks)
(b) The student then increases the pulling force to \( 10 \text{ N} \). Assuming the frictional force remains the same as in part (a), calculate the net force acting on the block. (1 mark)
(c) Using the formula \( F = ma \), calculate the acceleration of the block when the pulling force is \( 10 \text{ N} \). (1 mark)