A 3.0-kg mass is dropped from the edge of a 50-m tall building with an initial s

Question

A 3.0-kg mass is dropped from the edge of a 50-m tall building with an initial speed of zero. The mass strikes the ground with a downward velocity of 25 m/s. Find the change in mechanical energy of the mass caused by air resistance between the point where it is dropped and the point where it strikes the ground? A. -0.46 kJ B. -0.53 kJ C. -0.61 kJ D. -0.38 kJ E. -0.81 kJ The escape speed from the surface of the Earth is 11.2 km/s. Estimate the escape speed for a spacecraft from the surface of the Moon. The Moon has a mass 1/81 that of Earth and a radius 0.25 that of Earth. A) 2.5 km/s B) 4.0 km/s C) 5.6 km/s D) 8.7 km/s Constants: G=4.67 times l0^-11 N m^2/kg^2 mu_0 = 1.26 times 10^-6 T m/A e-= 1.60 times 10^-19 C epsilon_0 =8.85 times 10^-12 C^2/N m^2 M_E = 5.98 epsilon 10^24 kg R_E = 6.38 times 10^6 m k=8.99 times 10^9 Nm^2/C^2

Explanation / Answer

11.

From Work Energy theorem,

Wnet = change in Energy

chnage in energy = mgh - 0.5 mv^2

dE = (3 * 9.81* 50) -(0.5 *3 * 25^2)

dE = -0.534 K J

option B
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12.

Formula for Escape Vesc = sqrt2 * GM/r

Vesc = sqrt2 * 6.67*10^-11 * (M/81)/(0.25* r)

Vesc = sqrt 2 * GM/r * 1/(81* 0.25)

Vesc = 11.2 * 1000* 1/(81* 0.25)

Vesc = 2.5 km/s

option A it is

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