# Solving for Acceleration when weight is in Newtons instead of Kg

## Homework Statement

On the earth, an astronaut and the equipment weigh 1,960 N. Weightless in space, the motionless astronaut and equipment are accelerated by rocket pack with
100 N thrust, that fires for 2.0s. What is the resulting final velocity? (Hint: First calculate the acceleration. Also take the initial velocity as zero)

## Homework Equations

I am not sure how to solve for the Acceleration when mass is in Newtons and not Kg. I can not use the formula which I think i use which is f=ma. then the final velocity = acceleration * time - initial velocity

## The Attempt at a Solution

I divided 1960 N by 9.8 m/s^2= 200kg <<If that is right please explain because I don't understand.

200kg * a = 100N which equals a=0.5m/s^2

Vf = 0.5m/s^2 * 2sec - 0 = 1m/sec for the final velocity.

## Answers and Replies

Weight is a force, measured in newtons. Mass is, well, mass, measured in kg. You must get the distinction clear.

i know but the problem has given me a weight of the astronaut and his equipment in newtons not in kg so how can i solve for the acceleration

haruspex
Science Advisor
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tms is pointing out the misuse here: "when mass is in Newtons and not Kg".
You are told the weight at Earth's surface in N, not the mass. From that you correctly deduced the mass.

I think i got it now. But one more question, so is that always how you would change the newtons into a mass in kg by dividing it by the acceleration due to gravity or is there a formula to manipulate.

haruspex
Science Advisor
Homework Helper
Gold Member
2020 Award
is that always how you would change the newtons into a mass in kg by dividing it by the acceleration due to gravity
Yes. Weight is only meaningful in a specified context (i.e. the local gravitational field) and is given by mass * field strength. So given the weight you can divide by the field strength to get the mass.

okay well thanks guys the rest should be right then.