Physics Work and Energy, Momentum

posted by .

Let g be the acceleration due to gravity at the surface of a planet of radius R. Which of the following is a dimensionally correct formula for the minimum kinetic energy K that a projectile of mass m must have at the planet's surface if the projectile is to escape from the planet's gravitational field?
A) K=sqt.(gR)
B) K=mgR
C) K=mg/R
D) K=m*sqt.(g/R)
E K=gR

(I thought the answer should be K=mgR/2, but the key is B)... )


The sum of all the extenral forces on a system of particles is zero. Which of the following must be true of the system?
A)the total mechanical energy is constant
B)total potential energy is constant
C)total kinetic energy is constant
D)total linear momentum is constant
E) it is in static equilibrium

I am so confused of these kind of question. How can I do these kind of problem? And when I see a problem, how can I figure out which method to use, momentum conservation or energy conservation, is easier? Is any characteristics?

Thanks!



Any helps??????????????
Please.............

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. PHYSICS HELP PLEASE!!!

    A block of mass 2.62 kg is kept at rest as it compresses a horizontal massless spring(k = 141 N=m) by 15.3 cm. As the block is released, it travels 0.627 m on a rough hori- zontal surface before stopping. The acceleration of gravity …
  2. Physics/Math

    Ok...I figured out part a but I am having trouble with b. part a was: Zero, a hypothetical planet, has a mass of 1.0x10^23 kg, a radius of 3.0x10^6 m, and no atmosphere. A 10 kg space probe is to be launched vertically from its surface. …
  3. Physics Thanks

    Please help... Let g be the acceleration due to gravity at the surface of a planet of radius R. Which of the following is a dimensionally correct formula for the minimum kinetic energy K that a projectile of mass m must have at the …
  4. physics

    An object rests on the surface of planet y. Its mass is unknown. Find the acceleration due to gravity near the surface of planet y. Answer in m/s/s. G=6.673x10^-23 radius of planet y=2439700m mass of planet y=3.302x10^23kg radius of …
  5. Physics- PLEASE HELP

    A 10.0 kg cylinder rolls without slipping on a rough surface. At an instant when its center of gravity has a speed of 16.0 m/s, determine (a) the translational kinetic energy of its center of gravity.(b) the rotational kinetic energy …
  6. physics

    An astronaut is on the surface of planet whose air resistance is negligible. To measure the acceleration due to gravity(g) he throws a stone upwards. He observe that the stone reaches the surface to a maximum ht of h =10m(which is …
  7. mechanics

    please help solve these questions (1a). The gravitational field strength g on the earth’s surface is 9.8N/kg. explain what this means.(b) Using the law of gravity, show that gr2= k. Where g=gravitational field strength at a distance …
  8. mechanics

    please help solve these questions (1a). The gravitational field strength g on the earth’s surface is 9.8N/kg. explain what this means.(b) Using the law of gravity, show that gr2= k. Where g=gravitational field strength at a distance …
  9. physics

    Question Part Submissions Used A 11.5-kg cylinder rolls without slipping on a rough surface. At an instant when its center of gravity has a speed of 10.9 m/s, determine the following. (a) the translational kinetic energy of its center …
  10. Science (energy)

    1. What similarities do nuclear energy and chemical energy share?

More Similar Questions