A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are neglected, the forcerequired to keep
1 answer:
Answer:
Zero Newtons
Explanation:
Newton's second law of motion states that the net force applied to an object is equal to the product between the object's mass and its acceleration:
In this case, we want the hockey puck to slide at constant velocity - constant velocity means zero acceleration:
a = 0
And so this means also that the net force is zero:
F = 0
However, the problem says that ice friction and air resistance are negligible - so there are no forces acting on the hockey puck. This means that the puck will continue its motion at constant velocity if we don't apply any other force on it.
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Answer:
Work out = 28.27 kJ/kg
Explanation:
For R-134a, from the saturated tables at 800 kPa, we get
= 171.82 kJ/kg
Therefore, at saturation pressure 140 kPa, saturation temperature is
= -18.77°C = 254.23 K
At saturation pressure 800 kPa, the saturation temperature is
= 31.31°C = 304.31 K
Now heat rejected will be same as enthalpy during vaporization since heat is rejected from saturated vapour state to saturated liquid state.
Thus, =
= 171.82 kJ/kg
We know COP of heat pump
COP =
=
= 6.076
Therefore, Work out put, W =
= 171.82 / 6.076
= 28.27 kJ/kg