What is the mass of this object?

[chengbin]

Homework Statement

A net force of 200N is applied to an object, causing its velocity to change from 30km/h to 20km/h in 2.3s.

Homework Equations

What is the object's acceleration? What is its mass?

The Attempt at a Solution

I got the correct answer for acceleration (-1.2m/s^2), but I'm having trouble with finding the mass.

I'm getting 199kg (m = 200N/1.2m/s^2), but the answer key says 170g. How is that correct?

 

[Rick88]

200/1.2 does not equal 199.

The answer should indeed be about 170kg.
Check your calculations again.

 

[chengbin]

Thanks.

Apparently I can't use my calculator properly.

I guess 170g is probably a typo in the book.

 

[Rick88]

they probably meant 170kg.
I got 167.8kg, which approximated to two significant figures gives indeed 170kg.