Physics 11 Gavin and gabe

Physics

What is the formula for impulse?

Impulse (J) = Force (F) × Time (t)

How is impulse related to momentum?

Impulse is equal to the change in momentum (J = Δp)

What is the formula for momentum?

Momentum (p) = Mass (m) × Velocity (v)

What are the units for impulse and momentum?

Both are measured in kg·m/s or N·s.

How can you increase an object’s momentum?

Increase its mass or velocity.

What happens to momentum in a closed system?

It is conserved (total momentum before = total momentum after)

Why do airbags and padding help reduce injury?

They increase the time over which force is applied, reducing the impact force.

 If a force of 50 N acts on an object for 2 seconds, what is the impulse?

100 N·s

A 5 kg object moving at 4 m/s comes to a stop. What is its change in momentum?

-20 kg·m/s (final momentum is 0, so Δp = 0 - 20 = -20 kg·m/s).

 How does a longer impact time affect force?

It reduces the force needed to change momentum

What does the law of conservation of momentum state?

The total momentum of a closed system remains constant unless acted upon by an external force.

What is the formula for momentum conservation in a two-body system?

What is an example of momentum conservation in everyday life?

A person jumping off a boat causes the boat to move in the opposite direction.

How does momentum conservation apply in collisions?

The total momentum before and after a collision remains the same, assuming no external forces.

What are the two types of collisions in momentum conservation?

Elastic and inelastic collisions.

What is an elastic collision?

 A collision where kinetic energy and momentum are both conserved. Objects bounce off each other.

What is an inelastic collision?

A collision where momentum is conserved, but kinetic energy is not. Objects may stick together.

Why does a gun recoil when fired?

To conserve momentum—momentum of the bullet moving forward is balanced by the backward recoil of the gun.

What happens when two ice skaters push off each other?

They move in opposite directions with equal and opposite momentum.

How does conservation of momentum apply in rocket propulsion?

The expulsion of gas downward creates an equal and opposite upward thrust, propelling the rocket forward.

How do you calculate acceleration (a) from initial and final velocity?

How do you calculate force (F) using acceleration?

A: a = (Vf - Vi) / t
a = (5.0 m/s - 13.0 m/s) / 2.5 s = -3.2 m/s²

A:
F = m a
F = 5.0 kg (-3.2 m/s²) = -16.0 N

How do you calculate acceleration when Vi = 0 and Vf = 72 m/s in 56 s?

How do you calculate force with mass and acceleration?

A:
a = (Vf - Vi) / t = 72 / 56 = 1.29 m/s²

A:
F = m a
F = (5.2 × 10⁴ kg) 1.29 m/s² = 6.7 × 10⁴ N

How do you calculate impulse (Δp)?

How do you calculate distance when Vi = 0?

A: Δp = m (Vf - Vi)
Δp = 0.055 kg (8.0 - 7.0 m/s) = 0.055 kg·m/s
Δp = 0.055 kg * (-16.5 m/s) = -0.825 kg·m/s

A:
d = ½ a t²
a = 1.29 m/s², t = 66 s
d = 0.5 1.29 66²
d = 2809.5 m = 2022.72 m (revised)

How do you calculate recoil speed of a rocket?

Can conservation of momentum be used to predict recoil?

A:
m₁v₁ = m₂v₂
v₁ = (m₂ v₂) / m₁
v₁ = (34 kg 770 m/s) / 1200 kg = -2.2 m/s

A:
Yes, as long as the rocket's mass is known.

Given m₁ = 450 g, m₂ = 160 g, Vi₁ = 32 cm/s, Vi₂ = 0, what's Vf₂?

What's Vi₁ if Vf₂ = 0.241 m/s?

A:
Vf₂ = (0.46 * 0.32) / (0.46 + 0.15) = 0.241 m/s

A:
Vi₁ = 0.072 / 0.45 = 0.16 m/s

How do you find final speed when m_box = 64000 kg at 2.22 m/s, m_train = 28000 kg at 1.39 m/s?

A:
(64000 2.22) + (28000 1.39) = (64000 + 28000) * Vf
Vf = 120640 / 92000 = 1.45 m/s
Converted to km/h: 5.22 km/h

Given m_car = 2200 kg at 15 m/s, m_truck = 5500 kg at 8 m/s:

A:
(2200 15) + (5500 8) = (2200 + 5500) * Vf
Vf = 11000 / 7700 = 1.45 m/s

How do you find force from momentum change?

A:
Δp = m Δv = 5 × 10⁴ kg 27.7 m/s = 1.39 × 10⁶ kg·m/s
F = Δp / t = (1.39 × 10⁶) / 60 s = 2.3 × 10⁴ N

What is the momentum of Jenny and her skateboard together if Jenny has a mass of 35.6 kg, the skateboard has a mass of 1.3 kg, and they are moving at 9.50 m/s?

351.3 kg·m/s (Momentum = (35.6 kg + 1.3 kg) × 9.50 m/s)

What impulse is given to a hockey puck if a force of 30.0 N is exerted on it for 0.16 s?

4.8 N·s (Impulse = Force × Time = 30.0 N × 0.16 s)

What speed does a 0.115 kg hockey puck reach if it starts from rest and is shot?

15.65 m/s

A 6.00 N force acts on a 3.00 kg object for 10.0 s. What is:

A) The object’s change in momentum?

b) Its change in velocity?

a) 60.0 kg·m/s (Impulse = 6.00 N × 10.0 s)

b) 20.0 m/s (Change in velocity = Impulse / Mass = 60.0 kg·m/s ÷ 3.00 kg)

A 600-kg object changes velocity from +10.0 m/s to +44.0 m/s in 68.0 s due to a constant force.

a) What is its change in momentum?

b) What is the magnitude of the force?

a) 20,640 kg·m/s (Momentum change = mass × velocity change)

b) 304 N (Force = Change in momentum ÷ Time)

A 845-kg race car accelerates from rest to 100 km/h in 0.90 s.

a) What is the change in momentum?

b) What average force is exerted on the car?

a) 23,472 kg·m/s (Momentum change = mass × velocity change)

b) 26,080 N (Force = Change in momentum ÷ Time)