some physics question(H2)
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Gravitation-
1)Calculate the gravitational potential of a point on the surface of the moon closest to the earth( ans : -3.9X10^6 J/kg)
Data : Mass of Earth : 6 X 10^24m
Mass of moon : 7.4 X 10^22m
radius of moon : 1.7 X 10^6
dist from centre of earth to centre of moon : 3.8 X 10^8
Dynamics-
2)A body, initially at rest, explodes into two pieces of mass 2m and 3m respectively. having a total kinetic energy E. What is the KE of the piece of mass 2M after the explosion? ans: 3E/5
3)A stationary ball of 6 X 10^-2 kg is hit horizontally with a tennis racquet. The bal is in contact in racquet for 30ms and leaves the racquet wif 27m/s
Calculate the horizontal distance travelled by the ball before it hits the ground, if it leaves the racquet at a vertical height of 2.5m.
thanks to those who can help -
1) GP due to earth+GP due to moon= -GM/(R-r)+-Gm/rOriginally posted by lavastar:Gravitation-
1)Calculate the gravitational potential of a point on the surface of the moon closest to the earth( ans : -3.9X10^6 J/kg)
Data : Mass of Earth : 6 X 10^24m
Mass of moon : 7.4 X 10^22m
radius of moon : 1.7 X 10^6
dist from centre of earth to centre of moon : 3.8 X 10^8
Dynamics-
2)A body, initially at rest, explodes into two pieces of mass 2m and 3m respectively. having a total kinetic energy E. What is the KE of the piece of mass 2M after the explosion? ans: 3E/5
3)A stationary ball of 6 X 10^-2 kg is hit horizontally with a tennis racquet. The bal is in contact in racquet for 30ms and leaves the racquet wif 27m/s
Calculate the horizontal distance travelled by the ball before it hits the ground, if it leaves the racquet at a vertical height of 2.5m.
thanks to those who can help
G=6.67^-11
M=Mass of Earth
m=Mass of moon
R=3.8 X 10^8
r=1.7 X 10^6
But my ans is -3.96X10^6 J/kg...Not the same as yours...but similar...Point out my mistake if you can
..Thkz
2) Ermmm... how to explain this...Logic? Proportion ba...Dunno how to explain to you
3) Impulse=Force x Time
=M A x Time
6 X 10^-2 x 27= 6 X 10^-2 x A x 30^-3
A=900 (OMFG) I'm wrong le ....
using S=ut+0.5at^2
t=0.714s
Using A=900, S=229m
This is my ans...Trying only...But i'm quite sure they can't help you...i'm only a E student for pre-lim
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Consider gravitational potential from both moon and EarthOriginally posted by lavastar:Gravitation-
1)Calculate the gravitational potential of a point on the surface of the moon closest to the earth( ans : -3.9X10^6 J/kg)
Data : Mass of Earth : 6 X 10^24m
Mass of moon : 7.4 X 10^22m
radius of moon : 1.7 X 10^6
dist from centre of earth to centre of moon : 3.8 X 10^8
Use formula -Gm/r
From earth,
gravitational potential = - 6.67e-11 * 6.0e24 / 3.8e8 = - 1.05e6
From moon,
gravitational potential = - 6.67e-11 * 7.4e22 / 1.7e6 = - 2.90e6
since gravitational potential is a scalar, you can add it up
answer = -3.95e6 J/kg -
For mathematical proof,Originally posted by lavastar:Dynamics-
2)A body, initially at rest, explodes into two pieces of mass 2m and 3m respectively. having a total kinetic energy E. What is the KE of the piece of mass 2M after the explosion? ans: 3E/5
initial momentum = 0
they will travel in opposite direction due to linear conservation of momentum in either x or y direction
to simplify matters,
2mv1 = -3mv2
v2 = -2/3 v1
0.5(2m)(v1)² + 0.5(3m)(v2)² = E
0.5(2m)(v1)² + 0.5(3m)(4/9)(v1)² = E
m(v1)² = 3E/5
so 0.5 (2m) (v1)² = 3E/5 -
G = 6.67 x 10^-11
for dragoncloud -
I think the 30ms and mass are not usedOriginally posted by lavastar:3)A stationary ball of 6 X 10^-2 kg is hit horizontally with a tennis racquet. The bal is in contact in racquet for 30ms and leaves the racquet wif 27m/s
Calculate the horizontal distance travelled by the ball before it hits the ground, if it leaves the racquet at a vertical height of 2.5m.
time taken to touch ground
0.5 (9.81) t² = 2.5
t = 0.7139
horizontal distance travelled = 27 * t = 19.3m -
sorry but u mind explaining the logic behind it ? why from earth, u use the dist from centre of earth to centre of moon but for moon, u use its radius?Originally posted by eagle:Consider gravitational potential from both moon and Earth
Use formula -Gm/r
From earth,
gravitational potential = - 6.67e-11 * 6.0e24 / 3.8e8 = - 1.05e6
From moon,
gravitational potential = - 6.67e-11 * 7.4e22 / 1.7e6 = - 2.90e6
since gravitational potential is a scalar, you can add it up
answer = -3.95e6 J/kg -
cos they want the GP on the surface on the moonOriginally posted by lavastar:sorry but u mind explaining the logic behind it ? why from earth, u use the dist from centre of earth to centre of moon but for moon, u use its radius? -
Technically speaking, you will have to consider from centre of earth to surface of moony. Thus, you can take the distance from centre of earth to centre of moon minus radius of moonOriginally posted by lavastar:sorry but u mind explaining the logic behind it ? why from earth, u use the dist from centre of earth to centre of moon but for moon, u use its radius?
However, the difference is extremely minute (100 times difference), and the final answer would not have been much different. -
What if the question is reversed?
Q) Calculate the gravitational potential of a point on the surface of the Earth closest to the moon.
How are we supposed to do this? -
simply reverse the calculationsOriginally posted by Darkness_hacker99:What if the question is reversed?
Q) Calculate the gravitational potential of a point on the surface of the Earth closest to the moon.
How are we supposed to do this?
However, I expect the moon's effect to be negligible compared to the earth's gravitional field.