# Physics

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Physics Homework
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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 -

I 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
t = [-5.6 +/- sqrt (31.4+2254)] / 9.8
= [ -5.6 + 47.8 ] / 9.8
= 4.31 seconds

• Physics -

By the way, for #5 look at my reply to Marina yesterday

• Physics -

THANX SOO MUCH!! YOU ARE AWESOME!!

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