# Question about the upthrust of a rocket

1. Dec 25, 2016

### ThatOneMidget

1. The problem statement, all variables and given/known data

The Saturn V rocket which launched the Apollo space missions had the following specifications: mass at lift-off = 3.0 x 10^6 kg velocity of exhaust gases = 1.0 x 10^4 m/s initial rate of fuel consumption at lift-off = 3.0 x 10^3 kg/s 1.(a) Calculate: (i) the force (thrust) produced at lift-off (ii) the resultant force acting on the rocket at lift-off

2. Relevant equations

Ft = mv

3. The attempt at a solution

i got the force exerted by the exhaust gases by rearranging the equation to F = mv/t. Upthrust was 33MN. But then i have no clue how to figure the second part out, the solution page says it is 3.6MN, i keep getting 3MN, any help would be greatly appreciated!

2. Dec 25, 2016

### Staff: Mentor

I don't see how you got the thrust value of 33 MN from the given information, notr how they arrived at 3.6 MN for the resultant force. Check the given value for the exhaust velocity: Was it perhaps a bit higher than 1.0 x 104 m/s?

3. Dec 25, 2016

### ThatOneMidget

4. Dec 25, 2016

### Staff: Mentor

5. Dec 25, 2016

### ThatOneMidget

I'm still getting 3MN for the net force, and 33MN for the upthrust

6. Dec 25, 2016

### ThatOneMidget

It seems like the book used 9.81 as a value for g although it stated to use 10 = g, anyways i've got it :D