Physics, 02.07.2019 16:10 CalCDanG

1. an object on earth and the same object on the moon would have a difference in
a. weight
b. mass
c. weight and mass
d. none of the above
2. how does doubling the mass of one object and tripling the distance between another object change the gravitational force between them?
fg = g m1 m2 / r2
a. force changes by 2/3
b. force changes by 2/9
c. force increases by 9
d. force decreases by 3
e. no change in force
3. according to the scientific definition of work, pushing on a rock accomplishes no work unless there is
a. a net force.
b. movement.
c. an opposing force.
d. movement in the same direction as the direction of the force.
4. a car going 30 mph has a kinetic energy of 10,000 joules. how much kinetic energy does it have if it goes 60 mph?
a. 40,000 joules
b. 10,000 joules
c. 5,000 joules
d. 2,500 joules
e. 20,000 joules
5. the specific heat of soil is 0.20 kcal/kgc° and the specific heat of water is 1.00 kcal/kgc°. this means that if 1 kg of soil and 1 kg of water each receive 1 kcal of energy, ideally,
a. the water will be 5°c.
b. the water will be warmer than the soil by 0.8°c.
c. the soil will be 5°c.
d. the water will warm by 1°c, and the soil will warm by 0.2°c.

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Answer from: naomijamieson88

Answers: (1) a. weight, (2)b. Force changes by 2/9, (3)b. movement, (4)a. 40,000 Joules, (5)c. the soil will be 5°C.

Answer 1: a. weight

Mass and weight are very different concepts.

Mass is the amount of matter that exists in a body, which only depends on the quantity and type of particles within it. This means mass is an intrinsic property of each body and remains the same regardless of where the body is located.

On the other hand, weight is a measure of the gravitational force acting on an object and is directly proportional to the product of the mass of the body by the acceleration of gravity :

W=m.g

Then, since the Earth and the Moon have different values of gravity, the weight of an object in each place will vary, but its mass will not.

Answer 2: b. Force changes by 2/9

According to the law of universal gravitation, which is a classical physical law that describes the gravitational interaction between different bodies with mass:

$F=G\frac{m_{1}m_{2}}{r^2}$ (1)

Where:

is the module of the force exerted between both bodies

is the universal gravitation constant

$m_{1}$ and $m_{2}$ are the masses of both bodies.

is the distance between both bodies

If we double the mass of one object (for example $2m_{1}$ ) and triple the distance between both (for example ). The equation (1) will be rewritten as:

$F=G\frac{2m_{1}m_{2}}{(3r)^2}$ (2)

$F=\frac{2}{9}G\frac{m_{1}m_{2}}{r^2}$ (3)

If we compare (1) and (2) we will be able to see the force changes by 2/9.

Answer 3: b. movement

The Work done by a Force refers to the release of potential energy from a body that is moved by the application of that force to overcome a resistance along a path.

When the applied force is constant and the direction of the force and the direction of the movement are parallel, the equation to calculate it is:

W=(F)(d)

Now, when they are not parallel, both directions form an angle, let's call it $\alpha$ . In that case the expression to calculate the Work is:

$W=Fdcos{\alpha}$

Therefore, pushing on a rock accomplishes no work unless there is movement (independently of the fact that movement is parallel to the applied force or not).

Answer 4: a. 40,000 Joules

The Kinetic Energy is given by:

$K=\frac{1}{2}mV^{2}$ (4)

Where is the mass of the body and its velocity

For the first case (kinetic energy $K_{1}=10000J$ for a car at $V_{1}=30 mph=13.4112m/s$ ):

$K_{1}=\frac{1}{2}mV_{1}^{2}$ (5)

Finding :

$m=\frac{2K_{1}}{V_{1}^{2}}$ (6)

$m=\frac{2(10000J)}{(13.4112m/s)^{2}}$ (7)

m=111.197kg (8)

For the second case (unknown kinetic energy $K_{2}$ for a car with the same mass at $V_{2}=60 mph=26.8224m/s$ ):

$K_{2}=\frac{1}{2}mV_{2}^{2}$ (9)

$K_{2}=\frac{1}{2}(111.197kg)(26.8224m/s)^{2}$ (10)

$K_{2}=40000J$ (11)

Answer 5: c. the soil will be 5°C

The formula to calculate the amount of calories is:

$Q=m. c. \Delta T$ (12)

Where:

is the mass

is the specific heat of the element. For water is $c_{w}=1 kcal/g\°C$ and for soil is $c_{s}=0.20 kcal/g\°C$

$\Delta T$ is the variation in temperature (the amount we want to find for both elements)

This means we have to clear $\Delta T$ from (12) :

$\Delta T=\frac{Q}{m.c}$ (13)

For Water:

$\Delta T_{w}=\frac{Q_{w}}{m_{w}.c_{w}}$ (14)

$\Delta T_{w}=\frac{1kcal}{(1kg)(1 kcal/g\°C)}$ (15)

$\Delta T_{w}=1\°C)}$ (16)

For Soil:

$\Delta T_{s}=\frac{Q_{s}}{m_{s.c_{s}}$ (17)

$\Delta T_{s}=\frac{1kcal}{(1kg)(0.20 kcal/g\°C)}$ (18)

$\Delta T_{s}=5\°C)}$ (19)

Hence the correct option is c.

Answer from: Quest

need to see circuit to get time constant

Answer from: Quest

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1. an object on earth and the same object on the moon would have a difference in
a. weight

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