A ball is thrown vertically upward, which is the positive direction. a little later it returns to its point of release. the ball
1 answer:
This motion of all can be divided in to two, first the upward motion and second downward motion.
In case of projectiles time taken for upward motion = time taken for downward motion.
So we have time taken for upward motion = 8.14/2 = 4.07 seconds
We have equation of motion, v = u+at, where v is the final velocity , u is the initial velocity, a is the acceleration and t is the time taken.
In case of upward motion
v = 0 m/s
t = 4.07 seconds
a = -9.8
Substituting
So initial velocity of ball = 39.886 m/s.
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Answer:
F = 2 × 10⁻³ N
Explanation:
Given:
frequency, f = 2400 MHz
Height, h = 25cm = 0.25 m
Area of the base, A = 30 cm x 30 cm = 900 cm² = 0.09 m²
Energy of the microwave, E = 0.50 mJ = 0.5 x 10⁻³ J
Now, the time taken by the wave from top to the base, t = h/c
here, c is the speed of the light
thus,
t = 0.25/(3 x 10⁸) = 8.33 x 10⁻¹⁰ s
The radiation pressure = Intensity/c
now, the intensity is given as:
I = Power/ area
also,
Power = Energy/ time = 0.5 x 10⁻³ J/8.33 x 10⁻¹⁰ s = 600000 W
thus,
I = 600000 W/ 0.09 m² = 6666666.6 W/m²
substituting the value in the formula for pressure due to radiation, we have
= 6666666.6 W/m²/(3 x 10⁸)
also
pressure = Force/ area
thus,
Force/ area = 6666666.6 W/m²/(3 x 10⁸)
or
Force (F) = (6666666.6 W/m² × 0.09 m²)/(3 x 10⁸)
or
F = 2 × 10⁻³ N