Linear Kinematics Problems

[Oracle]

Having problems with solving a few of these questions and some help which would be much appreciated.

 

 

1. A speed skater reduces her velocity from 12m/sec to 6m/sec in 5 seconds. Find:

 

a) acceleration

b) velocity at the end of the third second

c) average velocity

d) distance covered during the 5th second period

 

I found acceleration to be -1.2m/s^2 but I'm having trouble finding the distance traveled to work out velocity and the rest from there...

 

 

2. A sprinter covers the first 10 meters of a 100m dash in 2 seconds and the second 10 meters in 1.5 seconds. Find:

 

a) average velocities over the 0-10m and the 10-20m segments of the race.

ok so 0-10m v= 5m/s and 10-20m v= 6.6m/s

 

b) the acceleration between the first velocity and second velocity.

this is where I'm doing something wrong because I did 6.6-5/1.5-2 and I get -0.93 which is obviously wrong because the sprinter was not slowing down.

 

 

 

4. A ball is accelerating at 18m/s^2. The final velocity measurement used to determine the acceleration was 31m/s and the time was 0.42sec. What was the initial velocity of the ball at the start of the time interval?

 

Don't know how to find the initial velocity.

 

5. A sprint ice skater travels North at a 14m/sec, she must travel 100 meters to the North to complete the race. A cross wind blowing directly West at a constant 3m/s pushes the skater off course. If she does not correct for the wind:

 

a) how far off her Northerly path will she be blown?

b) How much extra distance must she cover to complete the race?

 

Again not sure about this problem.

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Anyone?..

 

I figured out q.3 with the formula d=Vi.t+1/2a.t^2 so don't worry about that one.

 

 

Still need help with the rest. Thanks

Edited March 18, 2010 by Oracle
Consecutive posts merged.

[swansont]

You need formulas for acceleration and average velocity, and a way to relate acceleration, velocity and time to each other. Do you know equations to do these things?

[Oracle]

I think I solved 2.b) Vf^2=Vi^2+2ad ---> 6.6^2=5^2+2a ---> 43.56=25+2a ---> 18.56/2 ---> a=9.28m/s^2

 

Does that looks right?

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You need formulas for acceleration and average velocity, and a way to relate acceleration, velocity and time to each other. Do you know equations to do these things?

 

Yeah I have a booklet here it's just applying the formulas gets tricky for me. I haven't got a text book yet for better explanations on things.

 

1. a) a= -1.2m/s^2

b) V at 3s = 10.8m/s

c) average Velocity = 3.6m/s

d) distance covered in 5th second = 18m

 

No idea if they are right... just need confirmation.

Edited March 22, 2010 by Oracle
Consecutive posts merged.

[swansont]

Not having an explanation of the equations is a problem, but you can find such things online. In the long run understanding the equations is a must.