What is the net force on a weather rocket during its flight?

[bcjochim07]

Homework Statement

A small rocket to gather weather data is launched straight up. Several seconds into the flight, its velocity is 120 m/s and it is accelerating at 18 m/s^2. At this instant, the rocket's mass is 48 kg and it is losing mass at the rate of .5 kg/s as it burns fuel. What is the net force on the rocket? Hint: Newton's second law was presented in a new form in this chapter

Homework Equations

p=mv F=dmv/dt F=dp/dt

The Attempt at a Solution

I tried to come up with a formula for momentum with respect to time and then differentiate it to find force, but it's not making sense to me.

I tried to say that at this instant dm/dt= -.5 and dv/dt = 18 and then I tried to multiply those but that clearly is not correct reasoning. I'm pretty sure I'm not looking at this problem right. Any hints?

 

[tiny-tim]

Welcome to PF!

I tried to say that at this instant dm/dt= -.5 and dv/dt = 18 and then I tried to multiply those but that clearly is not correct reasoning. I'm pretty sure I'm not looking at this problem right. Any hints?

Hi bcjochim07 ! Welcome to PF!

A hint? … yes! …

Product rule: d(mv)/dt = mdv/dt + vdm/dt.

 

[bcjochim07]

Oh yes, I see. Thank you very much!