A tennis ball is thrown from ground level with velocity directed 30° above the horizontal. if it takes the ball 0.5 s to reach t
1 answer:
The motion of the tennis ball on the vertical axis is an uniformly accelerated motion, with deceleration of 
(gravitational acceleration).
The component of the velocity on the y-axis is given by the following law:
At the time t=0.5 s, the ball reaches its maximum height, and when this happens, the vertical velocity is zero (because it is a parabolic motion):
. Substituing into the previous equation, we find the initial value of the vertical component of the velocity:
However, this is not the final answer. In fact, the ball starts its trajectory with an angle of
. This means that the vertical component of the initial velocity is
We found before
, so we can substitute to find 
, the initial speed of the ball:
The component of the velocity on the y-axis is given by the following law:
At the time t=0.5 s, the ball reaches its maximum height, and when this happens, the vertical velocity is zero (because it is a parabolic motion):
However, this is not the final answer. In fact, the ball starts its trajectory with an angle of
We found before
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Answer:
The reactance of the capacitor
Explanation:
In an AC circuit containing different elements (capacitors, resistors and inductors), we cannot simply calculate the equivalent resistance of the circuit, so another quantity is used, which is called reactance.
For a capacitor, the reactance is given by:
where:
f is the frequency of the AC current in the circuit
C is the capacitance of the capacitor
The reactance has a similar meaning to that of the resistance for a DC current. In fact, we notice that:
- When f=0 (which means we are in regime of DC current, because the current never changes direction), the reactance is infinite. This is correct: in a DC circuit, the capacitor does not let current pass through it, so it like it has infinite resistance (=infinite reactance)
- When f tends to infinite, the reactance becomes zero: in such situation, the current in the circuit changes direction so quickly that the capacitor has no enough time to "block" the current in the circuit, so it like it has almost zero resistance (zero reactance).