Newton's 2nd Law Rockets mit Gravity

If we fire a rocket vertically, its acceleration will be a bit less since it must struggle against gravity. For vertical ascent (neglecting air resistance):

• a_rocket = F_total ÷ m_rocket

If the rocket moves vertically, it sees (experiences) two forces:

1. the upward thrust of 120 Newtons
2. the weight of the rocket
   • weight = (rocket's mass) · (accel of gravity)
   • weight = 1.5kg · 9.8m/s²
   • weight ≈ 15N

Solution:

1. State the unknown: Acceleration
2. State the givens: Force and Mass
3. State the equation you plan to use: Acceleration = Force ÷ Mass
4. Plug in values with units of measure: Acceleration = (120N – 15N) ÷ 1.5kg
5. State your answer: 70 m/s²

Your Turn

A water bottle rocket has a mass of 0.248 kilograms. On Earth, this is a weight of 2.43 Newtons. When the water sprays out the bottom of the bottle rocket, it creates a starting thrust of 77 Newtons. Calculate the water rocket’s starting acceleration:

Solution:

1. State the unknown:
2. State the givens:
3. State the equation you plan to use:
4. Plug in values with units of measure:
5. State your answer:

Solution:

1. State the unknown: Acceleration
2. State the givens: Force and Mass
3. State the equation you plan to use: Acceleration = Force ÷ Mass
4. Plug in values with units of measure: Acceleration = (77N – 2.43N) ÷ 0.248kg
5. State your answer: 300m/s²