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Apparent weight in an elevator

You are standing on a bathroom scale in an elevator the is moving upward at constant speed, when suddenly the cable breaks. from just before to just after the cable breaks, the reading on the scale will be?

When the elevator is moving up with constant speed, the bathroom scale (weighing scale) shows the correct weight, because the mechanics involved will be the same if the frame is at rest or moving with a constant velocity.
When the cable breaks, it is a case of freely falling body and the scale reads zero.

A few numerical problems from laws of motion

  1. A worker pulls a 200. N packing crate with an applied force of 55.0 N.  The crate accelerates at a rate of 0.250  m/s(squared).  What is the coefficient of kinetic friction between the crate and the factory floor?
  2. A student pulls a 150. N sled up a 28 degree slope at a constant speed by applying a force of 100. N.  Near the top of the hill he releases the sled.  With what acceleration does the sled go down the hill?
  3. A 200. N crate rests on a ramp; the maximum angle just before it slips is 25 degrees with the horizontal.  What is the coefficient of static friction between the crate and the surface of the ramp?
  4. A man pulls a sled with a weight of 200. N with a constant velocity across a horizontal snow surface.  If a force of 80N is being applied to the sled rope at an angle of 53 degrees to the ground, what is the coefficient of friction between the sled and the ground?
  5. A jet plane is flying with  a constant speed along a straight line at an angle of 30degree  above the horizontal. The weight of plane is 86 500N. Its engine provides a forward thrust T of 103 000N. The lift of force L(directed perpendicular to the wings)and the force R of air resistance (directed opposite to the motion)act on the plane. Find L & R

Numericals from Class XI Physics Conservation of Momentum)

  1. A 41.0-kg boy, riding a 1.60-kg skateboard at a velocity of 5.70 m/s across a level sidewalk, jumps forward to leap over a wall. Just after leaving contact with the board, the boy’s velocity relative to the sidewalk is 6.00 m/s, 9.30° above the horizontal. Ignore any friction between the skateboard and the sidewalk. What is the skateboard’s velocity relative to the sidewalk at this instant?
  2. A 1.20-g bullet, traveling at a speed of 478 m/s, strikes the wooden block of a ballistic pendulum. The block has a mass of 191 g. (a) Find the speed of the bullet/block combination immediately after the collision. (b) How high does the combination rise above its initial position?
  3. After skiding down a snow-covered hill on an inner tube, Ashley is coasting across a level snowfield at a constant velocity of +3.0 m/s. Miranda runs after her at a velocity of +4.2 m/s and hops on the inner tube. How fast do the two of them slide across the snow together on the inner tube? Ashley’s mass is 71 kg, and Miranda’s is 58 kg. Ignore the mass of the inner tube and any friction between the inner tube and the snow.
  4. A car (mass = 1170 kg) is traveling at 28.8 m/s when it collides head-on with a sport utility vehicle (mass = 2580 kg) traveling in the opposite direction. In the collision, the two vehicles come to a halt. At what speed was the sport utility vehicle traveling?
  5. In an Atwood system mass 1= 2 kg and mass 2=7kg. The masses of the pulley and strings are negligible by comparison, the pulley turns without friction and the string does not stretch. The lighter object is released with a sharp push that sets into motion at v(initial)= 2.4 m/s downward.
    How far will m1 descend below it’s initial level?
    Find the velocity of m1 after 1.8 seconds

Why don’t we feel Earth’s Rotation?

Sreeda Asked:

“Why are we not feeling Earth’s rotation while it is actually happening”


It is just like we don’t feel like moving when we are inside  a train moving with constant velocity and especially when we are not looking out of the window.

When we look out from earth, we see stars and other heavenly bodies which are very much far away and the relative change in position is very much less to be noticeable.

The most celebrated test of Earth’s rotation is the Foucault pendulum first built by physicist Léon Foucault in 1851, which consisted of an iron sphere suspended 67 m from the top of the Panthéon in Paris. Because of the Earth’s rotation under the swinging pendulum the pendulum’s plane of oscillation appears to rotate at a rate depending on latitude. At the latitude of Paris the predicted and observed shift was about 11 degrees clockwise per hour. Foucault pendulums now swing in museums around the world.

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