Show Me The Physics - Recoil Problems

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Review - Explain this using one of Newton's Laws

A lead brick has a lot of mass
and therefore a lot of inertia.

The greater the mass, the greater the tendency for an object to remain at rest, the smaller the acceleration that is produced by a given force.

Conservation of Momentum

Newton Collider

B) Recoil Problem - When interacting objects start from rest

"What is the total momentum before
cannon is fired?"

"Total momentum after clown is fired?"

[ Flash ]

"Total momentum
before = 0. (at rest)

"Total momentum after
= 0. (momenta are
equal but opposite.)"

"In real life, it would be

foolish to shoot a rifle

like this. Why?"

"The recoil on that rifle

would throw the

shooter's shoulder out!"

Ex 1) A 4.0 kg rifle fires a
5.0 x 10^-3kg bullet at a velocity of 500. m/s.

What is the velocity acquired by the rifle?

Ex 1) A 4.0 kg rifle fires a 5.0 x 10^-3kg bullet at a velocity of 500 m/s. What is the velocity acquired by the rifle? (no shooter)

After rifle is fired

Rifle	Bullet
m_R=4.0 kg Rifle	m_B =5.0 x 10^-3 kg
V_R= ?	V_B = 500. m/s

Total Momentum Before =
Total Momenta After Interaction

0 = m₁V₁ + m₂V₂

Subtract m₂V₂ from both sides

m₁v₁ = - m₂V₂

In problem Solving, remove
negative sign and use

m₁v₁ = m₂v₂

(Not in Reference Table)

Ex 1) A 4.0 kg rifle fires a 5.0 x 10^-3kg bullet at a velocity of 500. m/s. What is the velocity acquired by the rifle?

Rifle	Bullet
m_R=4.0 kg	m_B =5.0 x 10^-3 kg
V_R= ?	V_B = 500. m/s

m₁v₁ = m₂v₂

(4.0 kg)V =(5.0x10^-3 kg)500.m/s

(4.0 kg)V = 2.5 kgm/s

V = .63 m/s

Momenta before/after= 0 before

Equal Mass

cars_explosion.mpg

W.F.U.

Total momentum after = 0 ??

carsExplosionUneq.mpg

W.F.U.

Yes, the slower cart has a greater mass

Ex 2) Two disk magnets are arranged at rest on a frictionless horizontal surface.

When the string holding them together is cut, they move apart under a magnetic force of repulsion.

a) What is the total momentum of the magnets before the string is cut?

Total momentum before = 0

(Both objects begin at rest)

b) What is the total momentum of the magnets after the string is cut?

Total momentum after = 0

(Total mom. before = Total mom. after)

c) What is the velocity of the 1.0 kg mass when the velocity of the 2.0 kg magnet is 30. m/s?

| Flash |

m₁ = 2.0 kg

m₂= 1.0 kg

V₂= ?

V₁= 30. m/s

m₁v₁ = m₂v₂

2.0 kg(30. m/s) = 1.0 kg(V)

V = 60. m/s

What is the velocity

of the cannon below?

m₁v₁ = m₂v₂

500 kg(V1) = 100 kg(15 m/s)

V₁ = 3 m/s

Recoil Problems - AP

Energy

Enrichment

http://www.wpclipart.com/

Rifle Recoil
Dr. Dave's Hall of Fame

Georgia Public Broadcasting Momentum Video