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antiseptic1488 [7]
3 years ago
7

A bus slams on its breaks and goes from 30 km/hr to 15km/hr in 4 seconds. What is its acceleration?

Physics
1 answer:
PolarNik [594]3 years ago
5 0

Acceleration = (change in speed) / (time for the change).

Change in speed = (15 - 30) = -15 km/hr
Time for the change = 4 sec

Acceleration = (-15 km/hr) / (4 sec) = -3.75 km/hr per second .

Is that a lot ?  Not much ?

Let's convert it to a unit that we can think about:

     (-15 km/hr) x (1,000 m/km) x (1 hr / 3,600 sec) =

           (-15 x 1,000) / (3,600)  =  -(4 and 1/6) m/sec .

So the acceleration of the bus is    -(4 and 1/6) m/sec² .

The negative sign means that it slowed down.

(4 and 1/6) m/sec²  is about  42%  of the acceleration of gravity ...
the acceleration the bus would have if it drove off of a cliff.

When the car or the bus you're riding in slows down at that rate,
you feel  42%  of your weight pulling you forward against your
seat belt.  That's quite a drastic acceleration !

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The vacuum pressure of a condenser is given to be 80 kpa. if the atmospheric pressure is 98 kpa, what is the gage pressure and a
dimaraw [331]

The absolute pressure is given by the equation,

P_{abs}=P_{atm}-P_{vac}

Here, P_{abs} is absolute pressure,P_{atm} is atmospheric pressure and P_{vac} is vacuum pressure.

Therefore,

P_{abs}=98 kPa-80 kPa=18kPa

The gage pressure is given by the equation,

P_{gage}=P_{abs}-P_{atm}.

Thus,

P_{gage}=18kPa-98 kPa=-80 kPa.

In kn/m^2,

The absolute pressure,

P_{abs}=18kPa(\frac{1kN/m^2}{kPa}) =18\ kN/m^2

The gage pressure,

P_{gage}=-80kPa(\frac{1kN/m^2}{kPa}) =-80\ kN/m^2.

In lbf/in2

The absolute pressure,

P_{abs}=18\ kPa(\frac{1.45\times 10^{-1}\ lbf/in^2 }{1kPa} )=2.6\ lbf/in^2

The gage pressure,

P_{gage}=-80kPa(\frac{1.45\times 10^{-1}\ lbf/in^2 }{1kPa} )=-11.6\ lbf/in^2

In psi,

The absolute pressure,

P_{abs}=18\ kPa(\frac{1.45037738\times 10^{-1}\ psi }{1kPa})=2.610\ psi.

The gage pressure,

P_{gage}=-80kPa(\frac{1.45037738\times 10^{-1}\ psi }{1kPa} )=-11.6030\ psi

In  mm Hg

The absolute pressure,

P_{abs}=18kPa(\frac{7.5\ mm\ of\ Hg }{1\ kPa})= 135\ mm\ of\ Hg

The gage pressure,

P_{gage}=-80kPa(\frac{7.5\ mm\ of\ Hg }{1\ kPa})=-600\ mm\ of\ Hg



3 0
2 years ago
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