Chapter 9 Flashcards
The SI units of momentum are
kg*m/s
If a body moves in such a way that its linear momentum is constant, then
the sum of all the forces acting on it must be zero
Two identical bodies of mass M move with equal speeds v. The direction of their velocities is illustrated in the figure. The magnitude of the linear momentum of the system is
(Sq. Rt. 2)Mv
A 40 kg girl standing at rest on the ice gives a 60 kg boy, who is also standing at rest on the ice a shove. After the shove, the boy is moving backward at 2 m/s. Ignore friction. The girl’s speed is
3 m/s
Two students, sitting on frictionless carts, push against each other. Both are initially at rest. The mass of Susan and her cart is M, and mass of Bob and his cart is 1.5M. If Susan pushes Bob so that she recoils with velocity -v, what is the velocity of Bob?
+2v/3
If the momentum of a mass M is doubled, its kinetic energy will be multiplied by a factor of
4
If you take the derivative of the kinetic energy of a particle with respect to its velocity you get
Momentum
Two mass M and 5M rest on a horizontal frictionless table with a compressed spring of negligible mass between them. When the spring is released, the energy of the spring is shared between the two masses in such a way that
M gets 5/6 of the energy
A golf ball and a Ping-pong ball are dropped in a vacuum chamber. When they have fallen halfway to the floor, they have the same
Speed
Impulse -
Average Force x Time = mass x delta velocity
Suppose a ping-pong ball and a bowling ball are rolling toward you. Both have the same momentum, and you exert the same force to stop each. How do the time intervals to stop them compare?
Both take the same time
Suppose a person jumps on the surface of Earth. The Earth
will recoil in the opposite direction with tiny velocity
What is the physical significance of the area under the curve of Force vs. Time?
Impulse
A 4.0 kg block, initially at rest, experiences a force that varies with time as shown in the figure. When t = 6.0 ms, the speed of the block is
3.0 m/s (if chart goes from 0-4 in 3.5s and 4-0 in 3.5-6 s)
A ball of mass m strikes a wall that is perpendicular to its path at speed +v and rebounds in the opposite direction with a speed -v. The impulse imparted to the ball by the wall is
-2mv
Two balls are dropped from a height of 6 m. Ball A bounces up to a height of 4 m whereas ball B bounces up to 2 m. Which ball experiences the larger impulse during its collision with the floor?
It is impossible to tell without knowing the masses of the balls.
In all collisions of short duration and for which it is true that no external forces act on the collision participants
Momentum is conserved
For a system consisting of two particles that undergo an elastic collision,
Both kinetic energy and momentum are conserved
Two cars of equal mass travel in opposite directions at equal speeds. They collide in a perfectly INELASTIC collision. Just after the collision, their velocities are
zero
Two equal masses travel in opposite directions with equal speed. If they collide in a perfectly ELASTIC collision, then just after the collision their velocities will be
Equal in magnitude but opposite in direction from their original velocities
Two equal masses travel in opposite directions with equal speed. If they collide in a collision that is between elastic and inelastic. Just after the collision, their velocities are
Less in magnitude and opposite in direction from their original velocities
The figure shows a ballistic pendulum in three states. Which of the following statements is true?
The total mechanical energy is conserved after the collision
Two particles m1 and m2 each with mass m are moving with velocity -v and 2v, respectively. The momentum of m1 relative to the center-of-mass is
-3/2mv
A man in a spacecraft that is moving with a velocity Vo in free space runs forward and then stops. The center o mass of the system (that is, the ship and the man)
Continues all the while at its original velocity
