About the nabla operator (∇) and the nabla dot (∇·), say if it is true or false:
1 In the heart, the current has an address.
2 The equationV=r, where r is the 3D distance from the origin, is a scalar function.
3 The nabla-dot operator can be used with V if V=r.
4 Geometrically, the nabla and nabla punto operators refer to the same.
5 In electric fields, the potential function is usually a vector.
6 If the current is described as a vector function, the operator calls point is greater at points where the current originates.
7 The nabla operator can be used in V if V=r.
8 Given a vector function, one can use the nabla operator and the nabla operator point in it.

Tom is having a problem with his washing machine. he notices that the machine vibrates violently at a frequency of 1500 rpm due to an unknown rotating unbalance. the machine is mounted on 4 springs each having a stiffness of 10 kn/m. tom wishes to add an undamped vibration absorber attached by a spring under the machine the machine working frequency ranges between 800 rpm to 2000 rpm and its total mass while loaded is assumed to be 80 kg. a) what should be the mass of the absorber added to the machine so that the natural frequency falls outside the working range? b) after a first trial of an absorber using a mass of 35 kg, the amplitude of the oscillation was found to be 10 cm. what is the value of the rotating unbalance? c) using me-3.5 kg.m, find the optimal absorber (by minimizing its mass). what would be the amplitude of the oscillation of the absorber?