Momentum & Impulse Review

A 4 kg block is traveling to the right at 6 m/s. It runs into a stationary 8 kg block. If the 4 kg block comes to a halt after the collision, what is the velocity of the 8 kg afterward, in m/s?

Mathematical Equivalence

OFF

Answer explanation

p₄ + p₈ = p₄ + p₈

(4)(6) + 0 = 0 + (8)v_f

24 = 8v_f

v_f = 3 m/s

Tags

NGSS.HS-PS2-2

Two ice skaters, of masses m and 2m, are standing on ice, at rest. Then they push off each other. If the 2m skater has a velocity of 12 m/s after the push, what is the speed of the m skater, in m/s?

Mathematical Equivalence

ON

Answer explanation

p_i = p_f

0 = p_m + p_2m

0 = mv_m + (2m)v_2m

0 = 12m + (2m)v_2m

-12m = 2mv_2m

-12 = 2v_2m

v_2m = -24 m/s

Problem says SPEED, so we provide the absolute value of our answer (24 m/s).

Tags

NGSS.HS-PS2-2

A 7 kg block is traveling with a velocity of 3 m/s. It runs into a 9 kg block, which was traveling with a velocity of −4 m/s. Which block, if either, will experience a greater magnitude of force during the collision?

• The 9 kg block

• The 7 kg block

• It depends on their velocities afterward

• Neither, both blocks will experience the same magnitude of force

Tags

NGSS.HS-PS2-2

A 8 kg block is initially traveling with a velocity of 7 m/s. It hits and bounces off a wall. Afterward, it has a velocity of −2 m/s. How much impulse did it experience during its collision, in Ns?

Mathematical Equivalence

ON

Tags

NGSS.HS-PS2-2

A 8 kg block is initially traveling with a velocity of 7 m/s. It hits and bounces off a wall. Afterward, it has a velocity of −2 m/s. What is the block's change in velocity during this collision, in m/s?

Mathematical Equivalence

OFF

Two ice skaters, of masses m and 2m, are standing on ice, at rest. Then they push off each other. Which skater, if either, will experience a greater magnitude of impulse from the push?

• The 2m skater

• The m skater

• It depends on their velocities afterward

• They will experience impulses of equal magnitude

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-2

I drop a text book off a 5 meter tall building. How fast is it traveling right before it hits the ground, in m/s?

Mathematical Equivalence

ON

Answer explanation

Ei = Ef

Ug = K

mgh = 0.5mv²

gh = 0.5v²

2gh = v²

v = √(2gh)

v = √(2(10)(5))

v = √100

v = 10 m/s

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-4

An asteroid slammed into the Earth and destroyed all of the dinosaurs. Which was greater in magnitude, force of Earth on asteroid, or asteroid on Earth?

• Asteroid on Earth

• Earth on asteroid

• Equal & opposite

• Depends on how many dinosaurs died

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-4

A 50 kg rider is traveling at 20 m/s and then comes to a halt. How long was the stop, in seconds, if the rider felt an average force of 4000 N acting upon them during the stop?

Mathematical Equivalence

ON

Tags

NGSS.HS-PS2-1

Object A is more massive than object B. It must have a greater momentum.

• True

• False

Answer explanation

p = mv

Mass matters, but so does the velocity. Unless we know the velocities of the two objects, we cannot determine which object has a greater momentum.

Tags

NGSS.HS-PS2-2