# Homework Help: Rocket Motion Problem

1. Apr 7, 2010

### TyErd

1. The problem statement, all variables and given/known data
What is the acceleration of the rocket at a time of 5seconds after the parachute opens.

2. Relevant equations
F=ma

3. The attempt at a solution
I simply thought the acceleration would be 9.8m/s/s

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2. Apr 7, 2010

### Staff: Mentor

That would be the acceleration acting downward if there were no parachute. The retarding force R of the parachute acts upward, in the opposite direction of the gravitational force acting on the rocket.

3. Apr 7, 2010

### Mintea

You also have to take into consideration the resistance force on the parachute; that will affect the acceleration.

4. Apr 7, 2010

### TyErd

so the resistance force of the parachute is 1.8N. So I know its going to be F-1.8=mass(which I forgot to mention but its 0.2kg) * acceleration., But how do I calculate the upwards acceleration

5. Apr 7, 2010

### Staff: Mentor

F = ma, so a = F/m. What's the net acceleration, and in what direction?

6. Apr 7, 2010

### TyErd

would the net acceleration be 1.8/0.2?

7. Apr 8, 2010

### Staff: Mentor

No, that's the acceleration upward. The net acceleration would be the vector sum of the upward and downward accelerations.

8. Apr 8, 2010

### TyErd

ohh so a=(9.8-1.8)/0.2