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vova2212 [387]
2 years ago
14

a body is dropped from a height of 240m. (i)How long does it take to reach the ground. (ii) What is the velocity with which it w

ill strike the ground.
Physics
1 answer:
kramer2 years ago
5 0

Answer:

7.0 s, 69 m/s

Explanation:

If we take down to be positive, then the time to reach the ground is:

x = x₀ + v₀ t + ½ at²

240 m = (0 m) + (0 m/s) t + ½ (9.8 m/s²) t²

t = 7.0 seconds

The final velocity is:

v² = v₀² + 2a(x - x₀)

v² = (0 m/s)² + 2(9.8 m/s²) (240 m - 0 m)

v = 69 m/s

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Answer:

5 hours

Explanation:

Let the required time be x hours. The time will be the same for both cars.

The cars will cover different distances because they are travelling at different speeds.

<em>D=S×T </em>

The distance travelled by the slower car = 50×x miles.

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A train traveling at 25 m/s is blowing its whistle at 440 Hz as it crosses a level crossing. You are waiting at the crossing and
ohaa [14]

Answer:

b) 472HZ, 408HZ

Explanation:

To find the frequencies perceived when the bus approaches and the train departs, you use the Doppler's effect formula for both cases:

f_o=f\frac{v_s+v_o}{v_s-v}\\\\f_o=f'\frac{v_s-v_o}{v_s+v}\\\\

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vs: speed of sound = 343m/s

vo: speed of the observer = 0m/s (at rest)

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f': frequency when the train is getTing closer.

Thus, by doing f and f' the subjects of the formulas and replacing the values of v, vo, vs and fo you obtain:

f=f_o\frac{v_s-v}{v_s+v_o}=(440Hz)\frac{340m/s-25m/s}{340m/s}=408Hz\\\\f'=f_o\frac{v_s+v}{v_s-v_o}=(440Hz)\frac{340m/s+25m/s}{340m/s}=472Hz

hence, the frequencies for before and after tha train has past are

b) 472HZ, 408HZ

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