- #1

sarmar

- 8

- 0

## Homework Statement

a) Cathy takes the bus home from work. In her hand she holds a 2.0kg cake box, tied together with a string. As she ascends the steps into the bus, the box accelerates upward at a rate of 2.5 m/s^2. What is the force exerted on the string?

## Homework Equations

F=ma

Fnet=Fg+FN

## The Attempt at a Solution

Fnet=Fg+FN

ma=Fg+FN

FN=ma-Fg

= (2.0)(2.5)-(2.0)(9.8)

= 5-19.6

=-14.6N

Therefore the force exerted on the string is 1.5x10N[upward]

-I am taking an independent physics course. I always do the question as best I can first, then I check this forum for verification, it helps so much. But for this question, it says that 24.6N is correct.

I followed the examples in my course book exactly so I don't know why it would be 24.6N.

I mean I understand how to get 24.6 but why would (2)(9.8)=19.6 turn negative if the box accelerates upward? Wouldn't it remain positive?

Or is 24.6 wrong? Confused.

Thanks in advance.