Gaokao Exam Physics: Mechanics and Kinematics 2

Question 1

A car accelerates uniformly from rest to 20 m/s in 5 seconds. What is its acceleration?

Accepted Answer

4 m/s²

Answer

Acceleration a = Δv/Δt = (20-0)/5 = 4 m/s².

Question 2

According to Newton's Third Law, when a horse pulls a cart forward, the cart pulls the horse backward with equal force. Why does the horse-cart system still accelerate forward?

Accepted Answer

Newton's Third Law action-reaction pairs act on different objects; the net force on the horse from the ground exceeds the backward pull from the cart

Answer

Action-reaction forces always act on different objects and cannot cancel each other. The horse accelerates because the ground pushes it forward (friction) more than the cart pulls it back. The NET force on the horse-cart system is analyzed separately.

Question 3

A 2 kg object slides down a frictionless incline of 30°. What is its acceleration along the incline? (g = 10 m/s²)

Accepted Answer

5 m/s²

Answer

The component of gravity along the incline: a = g·sin30° = 10 × 0.5 = 5 m/s². Mass cancels out.

Question 4

The unit of momentum in the SI system is:

Accepted Answer

kg·m/s

Answer

Momentum p = mv. Units: kg × m/s = kg·m/s. This is also equivalent to N·s (Newton-second), since N = kg·m/s².

Question 5

In projectile motion (抛体运动), what happens to the horizontal velocity component throughout the flight (ignoring air resistance)?

Accepted Answer

It remains constant

Answer

In projectile motion without air resistance, the horizontal direction has no force acting on it, so horizontal velocity remains constant throughout the flight (Newton's First Law).

Gaokao Exam Practice Test

Gaokao Exam Practice Test

Gaokao Exam Physics: Mechanics and Kinematics 2