I have some Physics problems, can anyone help?

Question

Heres are the problems:

1. --If one object has a greater speed than a second object, does the first necessarily have a greater acceleration? Explain, using examples.

2.--Can the velocity of an object be negative when its acceleration is positive? What about visa versa?

3.--A car slows down from 20m/s to rest in a distance of 85m. What was its acceleration, assumed constant?

4.--at highway speeds, a particular automobile is capable of an acceleration of about 1.6m/s. At this rate, how long does it take to accelerate from 80km/h to 110km/h?

Id greatly appreciate it if you can answer any of these problems.

1. --If one object has a greater speed than a second object, does the first necessarily have a greater acceleration? Explain, using examples.

2.--Can the velocity of an object be negative when its acceleration is positive? What about visa versa?

3.--A car slows down from 20m/s to rest in a distance of 85m. What was its acceleration, assumed constant?

4.--at highway speeds, a particular automobile is capable of an acceleration of about 1.6m/s. At this rate, how long does it take to accelerate from 80km/h to 110km/h?

Id greatly appreciate it if you can answer any of these problems.

Answer 1

1. No

acceleration = (current speed - initial speed) / time

let us express in equations...as
first object: v1=u1+a1 t1
second object v2 = u2 + a2 t2

if v1>v2, then u1 could be higher than v2 and a1=0; hence a1 is not necessarily more than a2

2. Yes
again, v=u+at
if a>0, but u<0, then v can be less than 0.... so it depends on the starting velocity... it is a case of decreasing velocity....

3. v^2 = u^2 + 2 a s
0 = 400 + 2a (85) and hence a = - 40/17 m/s/s

4.left as homework
hint: convert units from km/h to m/s (multiply by 5/18)

Answer 2

1,2 and 3 already commented on by others.

4. Firstly 1.6 m/s is a speed, not an acceleration. Check the original question to see whether it was really 1.6 m/s/s ?

Assuming whoever wrote the question really meant 1.6m/s/s then you need to calculate how many meters per second difference in speed between 80 and 110kph and use change in velocity = acceleration*time (equivalently time=change in velocity / acceleration ) to find the number of seconds you need. Be sure to point out that this is the minimum time needed assuming that the car is heading in the same direction and accelerating at maximum rate all the time. ( 110 kph is just under 70 mph - is this legal where you live?)

I make it 5.2083 seconds but would express this as a less accurate answer given the 'about 1.6m/s/s' accuracy on acceleration. I could easilly have made a mistake though - what do you get?

Answer 3

1. Acceleration is a change in speed, usually upwards. Speed is a steady progression.

2. Relatively speaking yes. Case in point, when a rocket turns over in mid travel and starts slowing down.


For free help with school homework:


The Discovery Channel offers Cosmeo.com, while AOL has StudyBuddy.com. Then there is HomeworkSpot.com along with Ask for Kids (www.askforkids.com). Also, NationalGeographic.com/homewor... SparkNotes.com, FigureThis.org and Tutor.com and Brainfuse.com

Answer 4

1 The acceleration for both could be zero if the speed remains constant.
2 Yes.. a change of direction can also be an increase in accelleration.. you slow down to make a curve in your car but your acceleration increases