Answer:
14.3kg
Explanation:
Given parameters:
Quantity of heat = 149000J
Change in temperature = 5.23°C
specific heat of the ice = 2000J/kg°C
Unknown:
Mass of the ice in the bag = ?
Solution:
The heat capacity of a substance is given as:
H = m c Ф
H is the heat capacity
m is the mass
c is the specific heat
Ф is the temperature change;
since m is the unknown, we make it the subject of the expression;
m = H/ mФ
m = = 14.3kg
Answer:
15186 J energy lost due to friction
Explanation:
Given:
- Height of the tallest hill (first) h_1 = 16 m
- Height of the last hill h_2 = 7 m
- Velocity @tallest hill = 0
- Velocity @last hill = 0
Find:
How much energy was lost due to friction can be determined from an energy balance at point on top of tallest hill and on top of last hill:
E_p,1 + E_k,1 = E_p,2 + E_k,2 + E_f
Where, E_k,1 = E_k,2 = 0
E_p,1 - E_p,2 = E_f
E_f = m*g*(h_1 - h_2)
E_f = 172*9.81*(16 - 7)
E_f = 15186 J
Let k be the spring constant. Then you have
188=k*21.8
k=188/21.8=8.62,
In the second part you use
m g= k x
x=m g/k= 38/8.62=4.4cm
4.4 cm is the answer
Power dissipated by a resistor = (current)² x (resistance).
0.25 W = (0.02 A)² x (resistance)
This resistor = (0.25 W) / (0.02 A)²
This resistor = 625 ohms
If we want it to dissipate 0.5 W, then
0.5 W = (current)² x (625 ohms)
Current = √(0.5/625)
Current = √(0.0008)
<em>Current = 28.28 mA</em>
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A slightly easier way:
Since the power is = I²R, it grows in proportion to (current)² .
We want to double the power dissipated, so we only need to increase the current by the factor of √2 .
(20 mA) x (√2) = <em>28.28 mA </em>
The power transferred by the motor is equal to the product between the current and the voltage:
However, the power used by the winch system is less than this value. In fact, the work done is equal to the weight of the load times the distance through which it has been lifted:
And the power used by the system is the work done divided by the time taken:
Therefore, the efficiency of the system is given by the ratio between the useful power and the power in input: