# I need help with Newton's Laws

1. Mar 26, 2011

### sodium40mg

1. The problem statement, all variables and given/known data
Sorry to bother, but I was working through some homework I haven't done (I put a * next to ones I didn't get and I just wanted to post them because I have no idea how to do them):

1. If you are on a bus that is traveling along a straight, level road at 100 km/h, you are traveling at 100 km/h too.

(a) If you hold an apple over your head, how fast is it moving relative to the road? Relative to you?
(b) If you drop the apple, does it still have the same horizontal motion?

2. What is the advantage of the large flat sole on the foot of an elephant? Why must the small foot (hoof) of an antelope be so hard?

2. Relevant equations
Zip! These be word problems.

3. The attempt at a solution
1. (a) 100 km/h relative to road, 0 km/h relative to you

2. This doesn't even seem like a Newton's Law problem (hardness? what the?)

2. Mar 27, 2011

### JaWiB

If you drop the apple, what forces are acting on it? More specifically, are there any forces acting on the apple in the horizontal direction? How does force relate to change in velocity?

For 2) how much force is exerted on each of your feet while standing still? Does the answer change if you're standing on one toe of each foot? Would you rather stand on a single toe or your whole foot and why?

3. Mar 27, 2011

### sodium40mg

1) Force of gravity. In the horizontal direction? I would think no horizontal forces? I don't know how force relates to change in velocity?

2) Does this have to do with Force = Pressure / Area? I think your weight divided into 2 and exerts on both your feet, one one foot it's weight divided by 1. I would rather stand on my whole feet because there's more area, which means less force that I have to exert on my feet? I don't know?

4. Mar 27, 2011

### JaWiB

F = ma and a = change in velocity / time. Hence, if there is no force, there is no acceleration and there is no change in velocity.

Yup. So an elephant has big feet so that the force acts on a larger area. I wouldn't exactly call it a Newton's laws problem.