In Fig. 9-78, a 3.2 kg box of running shoes slides on a horizontal frictionless table and collides with a 2.0 kg box of ballet slippers initially at rest on the edge of the table, at height h = 0.40 m The speed of the 3.2 kg box is 3.0 m/s just before the collision. If the two boxes stick together because of packing tape on their sides, what is their kinetic energy just before they strike the floor?
The kinetic energy of the boxes just before they strike the floor, is 29 J .
i) Mass of running shoe box, .
ii) Mass of ballet slipper box, .
iii) Height of the table, .
iv) Speed of the mass , .
You can use the concept of conservation of momentum and conservation of mechanical energy. Using conservation of momentum, you find the initial velocity of the boxes at the edge of the table. Using conservation of mechanical energy, you can find the final velocity at the ground
First, we find the velocity of the boxes at the edge of the table; both move together, so they have the same velocity, v; we can say that v can be calculated using momentum conservation law as,
Now, this is the initial velocity for the next projectile motion. We know that both boxes initially have kinetic energy and potential energy, which will convert to kinetic energy at the ground.
Substitute the values in the above expression, and we get,
The kinetic energy of the boxes just before they strike the floor, .
Speed amplifier. In Fig. 9-75, block 1 of mass m1 slides along an x axis on a frictionless floor with a speed of .Then it undergoes a one-dimensional elastic collision with stationary block 2 of mass . Next, block 2 undergoes a one-dimensional elastic collision with stationary block 3 of mass . (a) What then is the speed of block 3? Are (b) the speed, (c) the kinetic energy, and (d) the momentum of block 3 is greater than, less than, or the same as the initial values for block 1?
In tae-kwon-do, a hand is slammed down onto a target at a speed of 13 m/s and comes to a stop during the 5.0 ms collision. Assume that during the impact the hand is independent of the arm and has a mass of 0.70 kg . What are the magnitudes of the (a) Impulse and (b) Average force on the hand from the target?
A shell is shot with an initial velocity of , at an angle of with the horizontal. At the top of the trajectory, the shell explodes into two fragments of equal mass (Fig.9-42). One fragment, whose speed immediately after the explosion is zero, falls vertically. How far from the gun does the other fragment land, assuming that the terrain is level and that air drag is negligible?
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