Water is used to cool down automobile engines when they get hot. Why is water used as a coolant?
2 answers:
Explanation :
Water is used to cool down automobile engines when they get hot. It is used as a coolant because it has a high heat capacity. It is approximately equal to .
The heat capacity of a substance is defined as the change in temperature due to the addition and removal of heat. Its SI unit is joule per kelvin. It is also an extensive property of matter.
The specific heat of water shows that each gram of water can absorb or release 4.186 joules of heat.
In the case of water, it will soak up a large amount of heat and its do not increase by very large amount.
So, the correct option is (d) "Water has a high heat capacity".
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Answer:
a) v² = v₀² + 2 g h, b) t = v₀/g (1+ √ (1 + 2gh/ v₀²))
Explanation:
a) This is an exercise that we can solve using conservation of energy.
Starting point. High point
Em₀ = K + U = ½ m v₀² + m gh
Final point. Soil
= K = ½ m v²
energy is conserved because there is no friction
Emo = Em_{f}
½ m v₀² + m g h = ½ m v²
v² = v₀² + 2 g h
b) the time it takes to reach the ground can be calculated with kinematics
let's create a reference frame with positive upward direction
v = vo - g t
when it reaches the ground it has a velocity v, the initial velocity is downwards v₀ = -v₀
v = -v₀ - gt
t = - (v + v₀) / g
we substitute the velocity values calculated in the previous part
t = - (√(v₀² + 2 g h) + vo) / g
we will simplify the equation a bit
t = - v₀/g (1+ √ (1 + 2gh/ v₀²))
c) is now thrown vertically upward with the same initial velocity vo.
To find the final velocity we use the conservation of energy where the velocity is squared, so it does not matter if it is positive or negative, therefore in this section the value should be the same as in part a
v = √ (v₀² + 2gh)
d) for this part if there is change since the speed is not squared
v₀ = v₀
v = v₀ - gt
t = (v₀ - v) / g
t = (v₀ - √(v₀² + 2 g h)) / g
t = v₀/g (1 - √(1 + 2gh / v₀²))
1. +72.0 kg m/s
The momentum of an object is given by:
p = mv
where
m is the mass of the object
v is its velocity
Taking "to the right" as positive direction, for Elena we have
m = 60.0 kg is the mass
v = +1.20 m/s is the velocity
So, Elena's momentum is
2. -162.5 kg m/s
Here Madison is moving in the opposite direction of Elena (to the left), so her velocity is
v = -2.50 m/s
while her mass is
m = 65.0 kg
Therefore, her momentum is
3. -90.5 kg m/s
The total momentum of Elena and Madison is equal to the algebraic sum of their momenta; taking into account the correct signs, we have:
4. 0.72 m/s to the left
We can find the final speed of Elena and Madison by using the law of conservation of momentum. In fact, the final momentum must be equal to the initial momentum (before the collision).
The initial momentum is the one calculated at the previous step:
while the final momentum (after the collision) is given by
where
is Elena's mass
is Madison's mass
v is their final velocity
According to the law of conservation of momentum,
So we can find v:
and the direction is to the left, since the sign is negative.