**Answer 1**

Since c asks for velocity of the car, I assume elastic collision

=====> KE and Mo are both conserved

Mot0 = MV = 4200 * 34 m/s = 142,800 kg - m/s

Mot1 = MV = 4200 * 22 = 92,400 kg - m/s

del Mo = 142,800 - 92,400 = 50,400

Moc1 = 50,400

Moc1 = MV = 900 * V = 50,400

V = 56 m/s

**Answer 2**Hello

You don't need to know if this is elastic or inelastic collision. You are only using the momentum equation, which applies to both.

Let Mt = mass of truck = 4200 kg

Mc = mass of car = 900 kg

Vti = Initial velocity of the truck = 34 m/s

Vci = Initial Velocity of the car = 0 m/s

Vtf = Final Velocity of the truck = 22 m/s

Vcf = Final Velocity of the car = ????

a) Initial Momentum of the truck (pti) = Mt*Vti

pti = 4200 kg * 34 m/s

pti = 142800 N-s

b) Final Momentum of the truck (ptf) = Mt *Vtf

ptf = 4200 kg * 22 m/s

ptf = 92400 N-s

c) Now for the fun part

Mt*Vti + Mc*Vci = Mt*Vtf + Mc*Vcf

Vci = 0

Mt*Vti = Mt*Vtf + Mc*Vcf

Mc*Vcf = Mt*Vti - Mt*Vtf

Mc*Vcf = Mt*(Vti - Vtf)

Vcf = (Mt/Mc)*(Vti - Vtf)

Vcf = (4200 kg/900 kg) * (34 m/s - 22 m/s)

Vcf = 56 m/s

Good Luck