Let her initial velocity be U.
Let the width of the river be W.
She swims 3/5 the width of the river at U.
Remainder width = (1 - 3/5) = 2/5.
She then swims 2/5 the width with velocity U/2.
Average Speed = (Total Distance Traveled) / ( Total Time Taken).
Distance = Speed * time
time = Distance / Speed.
Time in first trip: = (3/5)W / U = 0.6W/U.
Time in second trip = (2/5)W / (U/2) = 0.4W / 0.5 U = 0.8W/U
Total Distance Traveled = W, width of the river.
Average Speed = W / (0.6W/U + 0.8W/U) = W / (1.4W/U)
= W * U / 1.4W
= U/1.4
= U * 10 / 14
= (5/7) U.
Therefore Average speed is (5/7) of the initial speed.
<span>Acceleration of ball (a) = 9.8 m/s^2
Speed (v) = 24.5 m/s
Time (t) = Acceleration / Time
= v / a
= 24.5/9.8
= 2.5 s
So it will take 2.5 seconds to reach that speed.</span>
The answer is B hope this helped you !!
<h3><u>Answer</u> :</h3>
◈ As per newton's second law of motion, Force is defined as the product of mass and acceleration
Mathematically,
Unit of mass : kg
Unit of acceleration : m/s²
Therefore,
Unit of force ➠ <u>kg m/s²</u>
SI unit : <u>N (newton)</u> or <u>kg m/s²</u>
<u>Complete Question:</u>
Which of the following electromagnetic waves carries the highest energy, and are most damaging to human?
A. Gamma Rays
B. Microwave
C. Radio-wave
D. Alpha Rays
<u>Correct Option:</u>
Gamma Rays carries the highest energy, and are most damaging to human.
<u>Option: A</u>
<u>Explanation:</u>
The waves of light and other forms of energy that radiate or travel from where they are originated is understood as electromagnetic radiation, and collectively represent electromagnetic spectrum. The gamma rays are dangerous sources of radiation with high energy. Its standard size is 0.000001 nm i.e. size of atomic nucleus diameter. It results from the degradation of atomic nuclei by radioactive means. It is made up of the smallest electromagnetic wavelength, and thus provides the highest photon energy.
