# Homework Help: Physics Problems, could you tell me if I did them right?

1. Sep 17, 2009

### Ion1776

1. A parent pushes a baby stroller from home to daycare along a level road with a force of 38 N directed at an angle of 30° below the horizontal. If daycare is 0.83 km from home, how much work is done by the parent?

(38N)(cos(-30))(.83km or 830m)=????

2. You have a 0.750 kg picture frame on a mantle 1.50 m high. How much work was required to lift the frame from the ground to the mantle?

0.750*9.80=7.35N(1.50)=11.025 J

3. You lower a 2.50 kg textbook (remember when textbooks used to be made out of paper instead of being digital?) from a height of 1.81 m to 1.50 m. What is its change in potential energy?

1.81-1.50=.31
(2.50kg)(9.80)(.31)

=7.60 J

Please if someone could confirm these, plz be sure of the answer before responding, Thanks so much
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited: Sep 17, 2009
2. Sep 17, 2009

### Anden

The two last ones look correct, but your calculation on the first one doesn't make sense. Please explain, you're correct that E = F * d, but why is d = 10 km?

Wouldn't it be that d = 830 m and that F = 38 * cos 30? (cos 30 = cos -30) Then E = 27 kJ

3. Sep 17, 2009

### Ion1776

My equation is W=(Fcos(theta))(change is direction x)

is it (38)(cos(-30))(.83)=27.3144 J

4. Sep 17, 2009

### Anden

Haven't seen the above equation you're refering to before, but in the lower one: Remember, you must use 830 m and not 0,83 km, the definition of force is kg * m/s^2.

5. Sep 17, 2009

### Ion1776

alright.

Could someone else work these problems and confirm if i did them right

6. Sep 17, 2009

### Anden

I'm sorry, I'm a little confused. The formula (W = F cos(theta) * Change in direction) is the same as E = F * d, it's just a different notation.

I'm still curious where 10km came from though.

7. Sep 17, 2009

### Ion1776

You're correct dude i know, it was a keying error

8. Sep 17, 2009

### Ion1776

I just want multiple opinions on all these problems

9. Sep 17, 2009

### Anden

I understand, that's always a smart thing to do ;)