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July 7, 2015

July 7, 2015

Posted by **Ruby** on Sunday, July 20, 2008 at 1:08pm.

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1.) A particle at t 1 = -2.0 s is at x 1 = 3.4 cm and at t 2 = 4.5 s is at x2 = 8.5 cm. What is its average velocity? Can you calculate its average speed from this data?

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2.) A horse canters away from its trainer in a straight line, moving 160 m away in 17.0 s. It then turns abruptly and gallops halfway back in 6.8 s. Calculate:

(a) Its average speed

(b) Its average velocity for the entire trip, using “away from the trainer”, as the positive direction.

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3.) A car traveling 90 km/h is 100 m behind a truck traveling 75 km/h. How

long will it take the car to reach the truck?

4.) At highway speeds, a particular automobile is capable of an acceleration of about 1.6 m/s2. At this rate, how long does it take to accelerate from 80 km/h to 110 km/h?

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5.)Determine the stopping distances for an automobile with an initial speed of 90 km/h and human reaction time of 1.0 s:

(a) For an acceleration a = -4.0 m/s2;

(b) For a = -8.0 m/s2.

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6.) Calculate:

(a) How long it took King Kong to fall straight down from the top of the empire state building (380 m high)

(b) His velocity just before “landing”.

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7.) A kangaroo jumps to a vertical height of 2.55 m. How long was it in the air before returning to Earth? 0.26 s.

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8.) A helicopter is ascending vertically with a speed of 5.60 m / s. At a height of 115 m above the earth, a package is dropped from a window. How much time does it take for the package to reach the ground?

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Can someone please provide me the answers and explanations to these problems because i am completely lost. I would appreciate any help. thanx =) I am trying me BEST to understand physics. It really isn't working.

- Physics -
**Damon**, Sunday, July 20, 2008 at 1:38pmI am not going to just do all of these for you. I will do the cantering horse since it seems to be typical.

It goes +160 m in the first 17 seconds

Then it goes - 80 m in 6.8 seconds

so the distance it traveled was 160 + 80 = 240 m in 17+6.8 = 23.8 s

average SPEED = 240/23.8 m/s

Now its total displacement from the starting point is 160 - 80 = +80 m in those 23.8 seconds so its velocity is

+80/23.8 m/s

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Now that had no acceleration so I will do 8, the helicopter.

a = -9.8 m/s

v = Vo + a t = 5.60 - 9.8 t

h = Ho + Vo t + (1/2)at^2

so 0=115 + 5.6 t -4.9 t^2

that is a quadratic equation

t = [-5.6 +/- sqrt (31.4+2254)] / 9.8

= [ -5.6 + 47.8 ] / 9.8

= 4.31 seconds

- Physics -
**Damon**, Sunday, July 20, 2008 at 1:43pmBy the way, for #5 look at my reply to Marina yesterday

- Physics -
**Ruby**, Sunday, July 20, 2008 at 4:55pmTHANX SOO MUCH!! YOU ARE AWESOME!!

- big -
**juicy**, Thursday, September 16, 2010 at 3:18pmpen15