Physics Mid Term #2 (Ch.6-8)

the vector momentum is denoted with a …

p

formula for momentum is …

p = m x v

What are the units for momentum ?

kg & m/s

What is the formula for change in momentum ? Δp ?

Δp = p_f - p_o

Change in momentum is also called ?

impulse

What do p_f and p_o in the change in momentum formula each represent ?

p_f = after collision , p_o = before collision

Fnet (total force) = ?

Δp/ Δt

If Fnet = 0, that means that Δp/Δt = 0 , which means that Δp = 0 , which means that …

Δp_f = Δp_o

p_{o total or ( initial momentum total ) formula is ….}

p_o = m1v1_o+ m2v2_o

p_{f total or (final momentum total ) formula is ….}

p_f = m1v1_f + m2v2_f

What is the overall formula for the system relating to momentum ?

m1v1_o+ m2v2_o = m1v1_f + m2v2_f

If object is moving to the right add a ___ because that’s the positive direction.

+

What is the formula for this momentum system ?

m1v1_o-m2v2_o = (-) m1v1_f + m2v2_f

Even if Fnet = 0…the momentums of the objects in the system still ….

change ( ex. 4 + 4 = 8 but so does 3 +5 = 8 )

Before you apply conservation of momentum you must make sure…

there aren’t any external forces (only internal forces must be used / Fnet = 0)

Inelastic Collision formula …

p_o = p_f ( m1v1_o + m2v2_o = m1v1_f + m2v2_f)

Perfectly Inelastic Collision formula…

m1v1_o + m2v2_o = (m1 + m2) v_f

Elastic Collision formula…

p_o = p_f (m1v1_o + m2v2_o = m1v1_f + m2v2_f) and KE_o = KE_f (1/2m1v1_o² + 1/2m2v2_o² = 1/2m1v1_f² + 1/2m2v2_f²)

Ex) A 70-kg goalie originally at rest, collides with a 0.15kg puck at a velocity of 35 m/s. Suppose the goalie and the puck have an elastic collision and the puck is reflected back in the direction from which it came. What would be their final velocities ? What is the overall system velocity ?

v2_f = 34.9 m/s , v1_f = 0.15 m/s , v_system = 0.075 m/s