More acceleration practice , PLEASE HELP ME 1.A race car starts and finishes a race that is 50,000m. (30miles). The time is 23 minutes. The final velocity is 67m/s. What is the average acceleration?

2.The same car, after crossing the finish line, has a velocity of 45m/s. after 25 seconds. What was the acceleration for this time period?

3.The same car, after the time period in question 2, within 0.5 minute, slows to a constant speed of 20m/s. What was its acceleration for this time period? What is its acceleration after this 0.5 minute time period?

4.The same car, then follows a curve in the road at the same speed. Describe its acceleration. This same car then accelerates at 2m/s2. What will be its velocity after 10 seconds?

The answer is  a.first and third quarters 

    m₁v₁ + m₂v₂ = (m₁ + m₂)vmomentum is conserved.the left-hand side of the equation represents the momentum in the system before the collision.the right-hand side represents the momentum in the system after the collisionm₁ and v₁ represents the mass and the velocity of the physics blockm₂ and v₂ represents the mass and velocity of the ball of puttyv represents the final velocity of the combined mass.the question states the two masses stick together. they combined mass has its own velocity with the body mass the sum of the two objects' massestheir combined momentum is (m₁ + m₂)vto find the magitude of (m₁ + m₂)v, we need to add the vectors on the left-hand side of the equation: m₁v₁ + m₂v₂.note the diagram. i have positioned the vectors in accordance with their directions.the magnitude of the resultant can be calculated using the pythagorean theorem since this is a right triangle situation (north and west are perpendicular)|(m₁ + m₂)v| =  √[ (m₁v₁)² + (m₂v₂)² ]|(m₁ + m₂)v| =  √[ (1.5kg·8.0m/s)² + (0.40kg·20m/s)² ]|(m₁ + m₂)v| =  14.4 kg m/sfor two significant figures (assuming that 20m/s is two), this rounds to 14 kg m/s