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  1. J

    Theoretical Question: Mass of Earth

    I was just curious about this. Are humans counted in the mass of the Earth? If so as the population increases does the masss of the Earth also increase? I think it wouldn't due to humans technecally being made from the Earth. We are carbon, nitrogen, hydrogen, and oxygen from the Earth so when...
  2. J

    Dynamics and statics

    First break this into three parts of acceleration, constant speed, and decceleration. Change the 60km/hr into meters per second to get uniform units. Knowing the final velocity, the acceleration and the initial velocity of zero, use vf= v(initial) + at to find the time for the first part. Do the...
  3. J

    Friction problem

    I believe the above work is correct ecept that I don't believe its possible to have a negative coeffient of friction. Since friction itself is a retarding force, its inherently negative, thus it would look like (-2.45m)= -F thus the acceleration become positive.
  4. J

    Initial Velocity of a gun!Help please

    In this case, since the gun is told to be at a certain height, all the energy is potential, but its spring potential energy. Use E=(.5)kx^2 with k being the constant and x being the distance the spring is compressed. All this energy becomes linetic at the point of release so set it equal to the...
  5. J

    Basic kinematics

    if distance vs time gives you velocity, doing distance vs time gives you velocity, which vs. time gives you acceleration. slope of second graph is acceleration
  6. J

    Forces and friction :-s

    Knowing both mass and acceleration you should find fnet using F=ma. This value plus the frictional force must equal the applied force so simply use the mass to find the normal force to get frictional force.
  7. J

    Theoretical Range of a Rocket

    If you know the final distance in the y direction (60 meters), the acceleration(gravity), and the time, which is half time due to max height being at half the distance/time, you can find initial y velocity. Using this and the angle, find the intial x velocity.
  8. J

    More Work

    Its like punching a piece of paper. The paper works on you but you still break through. Relative to the paper, since the fist broke through, work is negative.
  9. J

    Easy Resultant Velocity Problem

    If he moves 10m/s and is slowed by 2.5m/s than how fast is the duck moving? Its the difference between the values. If confused draw vectors. That is it unless angles are involved.
  10. J

    Kinetic Energy

    Say KE=1 originally. It would become 2.25 if increased by a factor of 2.25. With the Equation KE=.5mv^2, you can isolate the v^2 to get v^2= KE/(.5m). Just replace the values and you would get that answer. 2.25/.5= 4.5 which becomes the square root of 4.5 after you square root velocity
  11. J

    Friction and the Coefficents of Friction question

    Floor is horizantal so normal force equals gravitational force. To break frictional force, applied force must equal it.
  12. J

    Potential and Kinetic Energy Problem

    Using the known distance, gravity, and the fact that its velocity is zero at its highest point you can find its final velocity
  13. J

    Forces with an angle

    Gravitational force equals the normal force on horizantal surfaces. Use that and the fact that it took 29N to break friction. At that point the applied force and frictional force is equal so frictional force is 29N. use that to find the coefficient. Same for the other one except with 23N
  14. J

    Please help to find mu, frictional force and normal force

    The body moves at 30 degrees so you need to use trig to break it into components at that angle. The force going down the ramp must equal the frictional force at the point friction breaks. The force going into the ramp is equal to normal and using both you can find coefficient of friction.
  15. J

    Sliding Object After a Push

    Since the applied force is horizantal, you can use the angle they give you to break it up into components. The force of the push going down the ramp plus the force of gravity down the ramp must equal the force of friction. Using that and the normal force, which you can find, you can find the...
  16. J

    Car rolling on an incline

    Use trig to break the car's force of gravity down into components. Find acceleration using F=ma and use the given distance to find final velocity.
  17. J

    Force question

    Use F=ma to find the force needed. a is 2 and m is 0.5. Then break the black's force of gravity into components qith trig. Subtract the force from F=ma from the force going down the ramp to get frictional force. The difference between the forces must be from friction. Simply find the normal...
  18. J

    Projectile Motion- Need help with equations to use for a falling object

    Paulie323 is correct. Plug his numbers into x(final)= x(initial) + v(initial)t + (1/2)(-9.8)t^2. Use quadratic. Simply plug in for t instead of x for 3.
  19. J

    How long does it take to reach the bottom of the ramp

    Draw a triangle and break the force of gravity into components using trigonomoetry. Knowing the distance and force you can find acceleration which you can use to find time.
  20. J

    Newtons 3rd law

    You are applying a force on the box in one direction. Nothing is applying a force on the BOX in the opposite dirrection you are. The force the box acts on us is countered by our muscles which force our body to stay in the spot we are.
  21. J

    Stockroom worker pushes a box homework problem

    If velocity is constant than all forces are equal. Force of friction will equal the applied force. Just do Force friction= normal fprce x coeddicient of kinetic friction. Since forces are equal they will be the same value.
  22. J

    Motion in one dimension

    If he goes 30m/s for 30 minutes, how many seconds are in 30 minutes. Find that and multiply. Then do the same for the next part.
  23. J

    Average Acceleration

    Show an attempt at the problem.
  24. J

    Projectile motion maximum range

    I'm assuming that since you do not have an angle, the problem is going on the basis that as you decrease your delta y, delta x increases. Think like this. Maximum range is always at 45 degrees, however since we don't know if the projectile was launched at 45 degrees, we must simply assume that...
  25. J

    2D Motion(Baby stuff but i )

    Using the final x position(120 meters) and the constant x velocity you found, you can find the time the ball be at that distance. Plug this time into the quation final vertical displacement= initial vertical displacemnt + (initial y-velocity x time) + (acceleration/gravity x time^2). if the...
  26. J

    Physics-gravitational forces

    force= mass x acceleration. weight= mass x gravity. in this case they would be the same
  27. J

    Elastic Collision Problem involving KE

    You could answer this question like, "If the two intial speeds are equal then..." and then answer the second part by saying, "If the initial speed of the lighter object is greater than that of the heavy object then..." and vce versa.
  28. J

    Equations of motion problem

    I calculated the same answers as Ambidext when I did the problem.
  29. J

    Equations of motion problem

    i see. the acceleration is negative. i did not see that. so the equation should be -(t)^2 +1.5t +1 . quadratic should give you two answers, one of which should work.
  30. J

    Equations of motion problem

    if i did the problem, it would become -1m= 0m + 1.5t + (1/2)2t^2. by moving the -1 over to the other side, i would use the quadratic formula dueto the equation becoming, t^2 +1.5t+1. (i just re-arranged it after moving the one over.
  31. J

    Equations of motion problem

    try using the equation final position= initial position + (initial velocity)(time) +1/2(acceleration)(time)^2. also try making the final position negative because it is below the starting point
  32. J

    Free fall, problem,

    If you're looking for the absolute minimum initial velocity, then at the end its velocity will be zero because at the apex of its flight the rock will be stationary for a split second where the naturalist can grab it.