# Homework Help: A 300 kg rocket sits on a launch pad. What is the thrust nee

Tags:
1. Mar 12, 2016

### j doe

1. The problem statement, all variables and given/known data
A 300 kg rocket sits on a launch pad. What is the thrust needed to obtain a thrust to weight ratio 3:1?

2. Relevant equations

3. The attempt at a solution
300.0 kg x 9.817 m/s2 = 2945.1 N

2. Mar 12, 2016

### BvU

Hello JD,
what do you think they mean with a thrust to weight ratio ?

3. Mar 12, 2016

### j doe

the amount of acceleration it needs in order to thrust an object with the mass of 300 kg?

4. Mar 12, 2016

### Kaura

I do not have much experience with this sort of equation but I believe that the equation for thrust to weight ratio is T/W where T is the force of the thrust and W is the weight of the given body measured in newtons hope this helps

5. Mar 12, 2016

### j doe

so based on your equation, would it be 3 / 2945.1 N? that would equal 0.00101864113. what would the units be?

6. Mar 12, 2016

### Kaura

I think you would have to find the force of thrust so that T/W would be equivalent to 3/1

7. Mar 12, 2016

### j doe

how do i do that?

8. Mar 12, 2016

### SteamKing

Staff Emeritus
Do you know what a ratio is?

Here's an example:

The ratio of centimeters to meters is 100 to 1.

You are asked to find the thrust such that a thrust to weight ratio of 3 to 1 is obtained. You have already determined the weight of the rocket.

9. Mar 12, 2016

### j doe

do i multiply 2945.1 by 3? i'm not quite sure how to find the thrust.

10. Mar 12, 2016

### SteamKing

Staff Emeritus
weight = mass × acceleration due to gravity

You calculated the weight of the rocket in Post #1 (2945.1 N)

You want the thrust o this rocket to be 3 times its weight.

Therefore, the thrust = ?

11. Mar 12, 2016

### j doe

thrust = 2945.1 N x 3 = 8835.3 N?

12. Mar 12, 2016

### Kaura

I believe that that is correct

If this is the case then excellent job

13. Mar 12, 2016

### SteamKing

Staff Emeritus
That looks OK.