Which is the best example of the law of conservation of energy?
a) a basketball stops bouncing because its energy disappears.
b) a rolling skateboard slows down because some of its kinetic energy changes to heat.
c)a falling book hits the ground and all of its energy is destroyed.
d)a toy car gains speed as it moves down a ramp because the ramp creates energy.

B) A rolling skateboard slows down because some of its kinetic energy changes to heat.

Explanation:

As we know by the law of conservation of energy that energy neither be created nor it can be destroyed but energy can convert from one form to another form.

So here we can say that in all such examples where energy is converted into one form to other form is an example of energy conservation

so here when we say that rolling skateboard slows down then in that case the kinetic energy of skateboard must have to convert into another form of energy. Since that energy is given in form of heat energy so this is a correct example of energy conservation.

so correct answer will be

B) A rolling skateboard slows down because some of its kinetic energy changes to heat.

a solenoid is created by wrapping a l = 90 m long wire around a hollow tube of diameter d = 4.5 cm.   the wire diameter is d = 0.9 mm.   the solenoid wire is then connected to a power supply so that a current of i = 9 a flows through the wire.

randomized variablesl = 90 m

d = 4.5 cm

d = 0.9 mm

i = 9 a                                          

write an expression for the number of turns, n, in the solenoid. you do not need to take into account the diameter of the wire in this calculation.

calculate the number of turns, n, in the solenoid.

write an expression for the length of the solenoid (l2) in terms of the diameter of the hollow tube d.

calculate the length of the solenoid (l2)   in meters.

calculate the magnitude of the magnetic field at the center of the solenoid in teslas.

explanation: