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Vesna [10]
3 years ago
9

If only an external force can change the velocity of a body, how can the internal force of the brakes bring a car to rest? 1. It

is the driver, not the car itself who causes the breaking, so it is an external force. 2. The engine is stopped, so the car has no force to run further. 3. Some internal forces can change the velocity of a body. 4. It is the force of the road on the tires (an external force) that stops the car.
Physics
1 answer:
RoseWind [281]3 years ago
3 0

Answer:

4. It is the force of the road on the tires (an external force) that stops the car.

Explanation:

If there is no friction between the road and the tires, the car won't stop.

You can see this, for example, when there is ice on the road. You can still apply the brakes (internal force), but since there is no friction (external force) the car won't stop.

The force of the brakes on the wheels is not what makes the car stop, it is the friction of the road against still tires that makes it stop.

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babymother [125]

Answer:

630.75 j

Explanation:

from the question we have the following

total mass (m) = 54.5 kg

initial speed (Vi) = 1.4 m/s

final speed (Vf) = 6.6 m/s

frictional force (FF) = 41 N

height of slope (h) = 2.1 m

length of slope (d) = 12.4 m

acceleration due to gravity (g) = 9.8 m/s^2

work done (wd) = ?

  • we can calculate the work done by the boy in pushing the chair using the law of law of conservation of energy

wd + mgh = (0.5 mVf^2) - (0.5 mVi^2) + (FF x  d)

wd = (0.5 mVf^2) - (0.5 mVi^2) + (FF x  d) - (mgh)

where wd = work done

m = mass

h = height

g = acceleration due to gravity

FF = frictional force

d = distance

Vf and Vi = final and initial velocity

wd =  (0.5 x 54.5 x 6.9^2) - (0.5 x 54.5 x 1.4^2) + (41 x 12.4) - (54.5 X 9.8 X 2.1)            

wd = 630.75 j

3 0
3 years ago
Calculate the wavelength of violet light with a frequency of 750×10 to the 12
MaRussiya [10]
Wavelength of any wave = (speed) / (frequency)

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Wavelength = 3 x 10 to the 8 / 750 x 10 to the 12 = 4 x 10 to the -7 or 400 nanometers.
3 0
3 years ago
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A building is being knocked down with a wrecking ball, which is a big metal sphere that swings on a 12-m-long cable. You are (un
leva [86]
Because you know that gravity is in m/s^2 so, period will be measured in seconds. You know the cable is 12m long and gravity is 9.81 solve for T (period) 2π12sqrt(9.81)=6.94922
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RUDIKE [14]

Answer:

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Explanation:

Given:

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Find:

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Friction force = 10 N

Coefficient of friction = Friction force / Force applied

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