B
Think of inertia of getting into a car accident without a seat belt although the car stops you will not you would likely fly out the window
By Newton's second law, the net force on the object is
∑ <em>F</em> = <em>m</em> <em>a</em>
∑ <em>F</em> = (2.00 kg) (8 <em>i</em> + 6 <em>j</em> ) m/s^2 = (16.0 <em>i</em> + 12.0 <em>j</em> ) N
Let <em>f</em> be the unknown force. Then
∑ <em>F</em> = (30.0 <em>i</em> + 16 <em>j</em> ) N + (-12.0 <em>i</em> + 8.0 <em>j</em> ) N + <em>f</em>
=> <em>f</em> = (-2.0 <em>i</em> - 12.0 <em>j</em> ) N
Answer:
![f=140\ N](https://tex.z-dn.net/?f=f%3D140%5C%20N)
Explanation:
Given:
- mass of the object on a horizontal surface,
![m=50\ kg](https://tex.z-dn.net/?f=m%3D50%5C%20kg)
- coefficient of static friction,
![\mu_s=0.3](https://tex.z-dn.net/?f=%5Cmu_s%3D0.3)
- coefficient of kinetic friction,
![\mu_k=0.2](https://tex.z-dn.net/?f=%5Cmu_k%3D0.2)
- horizontal force on the object,
![F=140\ N](https://tex.z-dn.net/?f=F%3D140%5C%20N)
<u>Now the value of limiting frictional force offered by the contact surface tending to have a relative motion under the effect of force:</u>
![F_s=\mu_s.N](https://tex.z-dn.net/?f=F_s%3D%5Cmu_s.N)
where:
normal force of reaction acting on the body= weight of the body
![F_s=0.3\times (50\times 9.8)](https://tex.z-dn.net/?f=F_s%3D0.3%5Ctimes%20%2850%5Ctimes%209.8%29)
![F_s=147\ N](https://tex.z-dn.net/?f=F_s%3D147%5C%20N)
As we know that the frictional force acting on the body is always in the opposite direction:
So, the frictional force will not be at its maximum and will be equal in magnitude to the applied external force and hence the body will not move.
so, the frictional force will be:
![f=140\ N](https://tex.z-dn.net/?f=f%3D140%5C%20N)
You didn't mention it, but the trumpeter herself has to be standing still.
<span>Person C, the one running towards the trumpeter, hears a pitch
that is higher than B-flat. (A)
Person B, the one running away from the trumpeter, hears a pitch
that is lower than B-flat.
Person D, the one standing still the whole time, hears the B-flat.</span>
The answer is Strontium(Sr)