Answer:
a) W = 46.8 J and b) v = 3.84 m/s
Explanation:
The energy work theorem states that the work done on the system is equal to the variation of the kinetic energy
W = ΔK =
-K₀
a) work is the scalar product of force by distance
W = F . d
Bold indicates vectors. In this case the dog applies a force in the direction of the displacement, so the angle between the force and the displacement is zero, therefore, the scalar product is reduced to the ordinary product.
W = F d cos θ
W = 39.0 1.20 cos 0
W = 46.8 J
b) zero initial kinetic language because the package is stopped
W -
=
-K₀
W - fr d= ½ m v² - 0
W - μ N d = ½ m v
on the horizontal surface using Newton's second law
N-W = 0
N = W = mg
W - μ mg d = ½ m v
v² = (W -μ mg d) 2/m
v = √(W -μ mg d) 2/m
v = √[(46.8 - 0.30 4.30 9.8 1.20) 2/4.3
]
v = √(31.63 2/4.3)
v = 3.84 m/s
Answer: Solar radiation reflects off the lighter colours, away from the car, thus keeping the car cool
Explanation: This is because lighter colors reflect a good amount of radiation while darker colors absorb it. Just like, Antarctica hasn't completely melted because it reflects a lot of the heat that is acting upon it. Or, you notice that you get hotter when you wear a black shirt opposed to a white one.
Energy to lift something =
(mass of the object) x (gravity) x (height of the lift).
BUT ...
This simple formula only works if you use the right units.
Mass . . . kilograms
Gravity . . . meters/second²
Height . . . meters
For this question . . .
Mass = 55 megagram = 5.5 x 10⁷ grams = 5.5 x 10⁴ kilograms
Gravity (on Earth) = 9.8 m/second²
Height = 500 cm = 5.0 meters
So we have ...
Energy = (5.5 x 10⁴ kilogram) x (9.8 m/s²) x (5 m)
= 2,696,925 joules .
That's quite a large amount of energy ... equivalent to
straining at the rate of 1 horsepower for almost exactly an
hour, or burning a 100 watt light bulb for about 7-1/2 hours.
The reason is the large mass that's being lifted.
On Earth, that much mass weighs about 61 tons.
The acceleration due to gravity on Earth is 9.8 m/s per second.
[Assuming that you've written 3.40 kg in 'a', and not 3.90 kg]
(a) 3,400 g x <u>0.001</u> = 3.40 kg [converting grams to kilograms]
(b) 220 cm x <u>0.01</u> = <u>2.2</u> m [converting centimeters to meters]
(c) 9.42 kg x <u>1000</u> = <u>9420</u> g [converting kilograms to grams]
(d) 6.53 m x <u>100</u> = <u>653</u> cm [converting meters to centimeters]