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Grade 9 Science — Quarter 4: Physics - Motion

Grade 9 Science Q4: projectile motion, momentum, and energy.

DepEd MELC reviewer for Grade 9 Science, Quarter 4. Master the concepts, tables, and common-mistake warnings below.

1

Projectile Motion

A projectile has constant horizontal velocity and accelerating vertical motion (gravity). The two are independent.

⚠️ Common Mistake

Horizontal and vertical motions are SEPARATE. Gravity only affects the vertical component.

2

Momentum and Impulse

Momentum p = mass × velocity  |  Impulse = Force × time = change in momentum
3

Conservation of Energy

Mechanical energy (KE + PE) is conserved in the absence of friction. As an object falls, PE converts to KE.

4

Worked Example

A 4 kg object moves at 5 m/s. Find its momentum and kinetic energy.

p = mv = 4 × 5 = 20 kg·m/s
KE = ½mv² = ½(4)(25) = 50 J

Momentum is a vector (it has direction); kinetic energy is a scalar measured in joules (J). Doubling the speed quadruples the kinetic energy because v is squared.

📌 Quick Recap — Master These

Before your test, make sure you can confidently do each of the following:

  • Explain and apply Projectile Motion.
  • Explain and apply Momentum and Impulse.
  • Explain and apply Conservation of Energy.
  • Explain and apply Worked Example.

Re-read any section above where you hesitate, then try the worked example again without looking.