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otez555 [7]
3 years ago
5

Suppose you want to operate an ideal refrigerator with a cold temperature of − 15.5 °C , and you would like it to have a coeffic

ient of performance of at least 8.25. What is the maximum hot reservoir temperature for such a refrigerator?
Physics
1 answer:
tensa zangetsu [6.8K]3 years ago
8 0

Answer:

15.65 °C

Explanation:

cold temperature (Tc) = -15.5 degree C = 273.15 - 15.5 = 257.65 kelvin

minimum coefficient of performance (η) = 8.25

find the maximum hot reservoir temperature of such a generator (Th)

η = \frac{Tc}{Th-Tc}

Th = Tc x (\frac{1}{η} + 1)

Th = 257.65 x (\frac{1}{8.25} + 1)

Th = 288.8 K

Th = 288.8 - 273.15 = 15.65 °C

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An RV is traveling 60 km/h along a highway. A boy sitting near the driver of the RV throws a ball to another boy at the back end
alina1380 [7]

Answer:

Speed of the ball relative to the boys: 25 km/h

Speed of the ball relative to a stationary observer: 35 km/h

Explanation:

The RV is travelling at a velocity of

v_{RV}=+60 km/h

Here we have taken the direction of motion of the RV as positive direction.

The boy sitting near the driver throws the ball back with speed of 25 km/h, so the velocity of the ball in the reference frame of the RV is

v_B = -25 km/h

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v = 25 km/h

Instead, a stationary observer outside the RV measures a velocity of the ball given by the algebraic sum of the two velocities:

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3 years ago
A 2000-kg truck is being used to lift a 400-kg boulder B that is on a 50-kg pallet A. Knowing the acceleration of the rear-wheel
anzhelika [568]

Answer:

(a) reaction at each front wheel is 5272N (upward)

(b) force between boulder and pallet is 4124N (compression)

Explanation:

Acceleration of the truck a_{t = 1 m/s^{2}  (to the left)

when the truck moves 1 m to the left, the boulder is B and pallet A are raised 0.5 m, then,

a_{A} =  0.5 m/s^{2} (upward) , a_{B} =  0.5 m/s^{2} (upward)

Let T be tension in the cable

pallet and boulder: ∑fy = ∑(fy)eff = 2T- (m_{A} + m_{B})g =  (m_{A} + m_{B})a_{B}

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Truck:  M_{R} = ∑(M_{R})eff: = -N_{f} (3.4m) + m_{T} (2.0m) - T (0.6m)= m_{T} a_{T} (1.0m)

Nf = (2.0m)(2000 kg)(9.81 m/s^{2} )/3.4m -  (0.6 m)(2320 N)/3.4m + (1.0 m)(2000 kg)(1.0 m/s^{2})  = 11541.2N - 409.4N - 588.2N = 10544N

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(b) force between boulder and pallet:

∑fy (upward) = ∑(fy)eff: N_{B} + M_{B}g - m_{B}a_{B}

            N_{B} = (400kg)(9.81 m/s^{2}) + (400kg)(0.5 m/s^{2}) = 4124N (compression)

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