physics help PLEASE?!?

Question

I DID do most of this homework, but these are the ones i did not get and could not find in the book. please answer any of them that you can that would really help!!!(if you can answer all of them esp.5 and 6 you can ge an easy 10 points :)

1.People not wearing seatbelts are sometimes hurt due to their_____?

2.two people travel from columbus to

3.In terms of positive,negative and zero acceleration, how would you describe the motion of a student in a cafeteria lunch line?Explain

4.If the net force acting on a body is 0, will the velocity be zero? Explain.

5. Vivian is walking to an appt. at 1.3 m/s she realizes she is late so she gradually increases her pace by .09 m/s^2. A)what is vivians speed after 10 s? B)at this speed is she walking jogging or running?

6.A torpedo is propelled through the water with a speed of 20 m/s, it explodes on impact with a target 2000 m away, If the sound is heard 101.4 s after the torped owas fired, what is speed of sound in the H2O?

i figured out 2 as i was typing, sorry!

Answer 1

1) momentum. Their body has momentum (it is in motion) and when the car hits something, the car loses its momentum but the person still has momentum, which means they are traveling 50mph inside the car, so instead of having their energy transfer into the flat belt across their chest, its tranfered through their face into the dash and steering wheel, which is much less comfortable. :)

2) ... Uhm... Argentina! (I think you forgot some of the question)

3) A person in a lunch line, when they are standing still, has zero acceleration. When they take a step they accelerate forward, and as they come to a stop they are accelerating backward ('negative'). If they are moving in the line at the same speed the whole time (if the line is moving continuosly) then they will accelerate forward until they match the speed/velocity of the line, and then stay at that speed (0 acceleration).

4) No. If the net force acting on a body is 0, that means that the body is not accelerating. The body could have been moving beforehand, though. For instance, a rock floating through space (with no gravity around) would have 0 net force, but would certainly be moving.

5) a) Using the equation that determines the velocity of an object with acceleration after t seconds: at + v0 = v, where t = 10s, a = 0.09ms^2 and v0 (pronounced vee-not) = 1.3m/s, its clear to see:

0.09m/s/s * 10s + 1.3m/s = 0.9m/s + 1.3m/s = 2.2m/s

2.2meters per second is just about 5miles per hour (I'll let you do the conversion), which I would call 'jogging' speed.

6) So we need to determine how long it took for the torpedo to get to the ship. Thats easy:

2000m = 20m/s * t
t = 100 seconds

If the total time is 101.4s, and it takes the torpedo 100.0s to get there, that means sound was traveling for 1.4s over the 2000m to get back. 2000m/1.4s = 1428.57m/s, or about 3200 miles per hour.

Good luck :)

Answer 2

1. Stupidity
2. ?
3. If they start and stop, then it's positive as they accelerate, then negative as they slow down, and zero when they're not moving.
4. No, an object already moving can have zero forces acting on it and it will continue to move until a force acts on it to stop it. It's one of newton's laws.
5. A. [10 * (.09) ] + 1.3 = 2.2 m/s. Convert to mph.
2.2 m/s * (3600s/hr) * (1km/1000m) * (1mi/1.6km) = 4.95mi/h
This is a jog.
6. This one is tricky. first you need to find out how long it takes the torpedo to reach the target.

Distance = Velocity * Time

2000m = 20m/s * T --> T = 100s

So if the torpedo hit 100s after being fired, but the sound was heard 101.4s after being fired, then that means it took the sound 1.4s to travel the distance, 2000m.

D=VT --> 2000m = V (1.4s) --> V = 1428.57 m/s