Mechanics key point

Question 1

What happens to a particle’s speed and velocity just before it hits the ground in free fall or projectile motion?

Answer 1

Speed = Maximum
→ Because the object has been accelerating due to gravity the entire way down.

Velocity = Minimum
→ Because velocity is a vector (has direction), and just before impact, it’s at its largest negative value (pointing downward).

Explanation:

Speed is the magnitude of velocity — always positive.

Velocity includes direction. Since the motion is downward, velocity becomes more negative.

So, numerically, velocity reaches its minimum value (most negative), while speed is at its peak.

Question 2

At maximum vertical height, which variable in SUVAT is 0

Answer 2

Velocity at t

Question 3

What do r and r0 represent

Answer 3

r is position vector (displacement as a vector)
r0 is initial position vector (Initial displacement as a vector)

Question 4

When is F≤μR and when is F=μR

Answer 4

Object at rest (ladders) 𝐹≤𝜇𝑅

Just about to move 𝐹=𝜇𝑅
(limiting) equilibrium

Already sliding 𝐹=𝜇𝑅
(kinetic)

F is never greater than 𝜇𝑅