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lesya [120]
3 years ago
10

A boy on a skateboard is pushed down the sidewalk by a friend. The skateboard rolls for a while but eventually comes to a stop.

What force is causing the skateboard to stop rolling?
Physics
2 answers:
Ket [755]3 years ago
4 0
Friction is causing the skateboard to stop rolling.
OLga [1]3 years ago
3 0
Friction is the force causing it
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A large fake cookie sliding on a horizontal surface is attached to one end of a horizontal spring with spring constant k = 440 N
irinina [24]

Answer:

a) 0.275 m b) 13.6 J

Explanation:

In absence of friction, the energy is exchanged between the spring (potential energy) and the cookie (kinetic energy), so at any point, the sum of both energies must be the same:

E = ½ kx2 + ½ mv2

If we take as initial state, the instant when the cookie is passing through the spring’s equilibrium position, all the energy is kinetic, and we know that is equal to 20.0 J.

After sliding to the right, while is being acted on by a friction force, it came momentarily at rest. At this point, the initial kinetic energy, has become potential elastic energy, in part, and in thermal energy also, represented by the work done by the friction force.

So, for this state, we can say the following:

Ki = Uf + Eth = ½* k*d2 + Ff*d

20.0J = ½ *440 N/m* d2 + 11.0 *d, where d is the compressed length of the spring, which is equal to the distance travelled by the cookie before coming momentarily at rest.

We have a quadratic equation, that, after simplifying terms, can be solved as follows, applying the quadratic formula:

d = -0.05/2 +/- √0.090625 = -0.025 +/- 0.3 = 0.275 m (we take the positive root)

b) If we take as our new initial status the moment at which the spring is compressed, and the cookie is at rest, all the energy is potential:

E = Ui = 1/2 k d²

In this case, d is the same value that we got in a), i.e., 0.275 m (as the distance travelled by the cookie after going through the equilibrium point is the same length that the spring have been compressed).

E= 1/2 440 N/m . (0.275)m² = 16.6 J

When the cookie passes again through the equilibrium position, the energy will be in part kinetic, and in part, it will have become thermal energy again.

So, we can write the following equation:

Kf = Ui - Ff.d = 16.6 J - 11.0 (0.275) m = 16.6 J - 3.03 J = 13.6 J

3 0
3 years ago
The density of a hippo is approximately 1030kg/m^3,so it sinks to the bottom of the freshwater lakes and rivers. A 1500kg hippo
hram777 [196]

Answer:

14,700 N

Explanation:

The hyppo is standing completely submerged on the bottom of the lake. Since it is still, it means that the net force acting on it is zero: so, the weight of the hyppo (W), pushing downward, is balanced by the upward normal force, N:

W-N=0 (1)

the weight of the hyppo is

W=mg=(1500 kg)(9.8 m/s^2)=14,700 N

where m is the hyppo's mass and g is the gravitational acceleration; therefore, solving eq.(1) for N, we find

N=W=14,700 N

8 0
3 years ago
Which piece of evidence did Alfred Wegener use to develop the theory of continental drift?
Eduardwww [97]
The right answer for the question that is being asked and shown above is that: "A.tectonic activity concentrated in certain areas." A piece of evidence did Alfred Wegener use to develop the theory of continental drift is that <span>A.tectonic activity concentrated in certain areas</span>
3 0
3 years ago
How to solve for the coefficient of friction
astraxan [27]
Their are two coefficients of friction, static and kinetic, regardless, they have basically the same formula:

u*N = F... aka
coefficient of friction*normal force = force of friction

Hope that helps!
3 0
2 years ago
What is the purpose of the lenses in a camera? a. Send light to the eyepiece c. Make the picture color or black and white b. Foc
aliya0001 [1]
The lenses on a camera focus the light entering the camera and provide a clear, sharp image at the location of the film or CCD device. If you took the lenses off a camera designed for use with lenses, you would not be able to create a usable image.
8 0
3 years ago
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