Suppose a 0.250-kg ball is thrown at 14.0 m/s to a motionless person standing on ice who catches it with an outstretched arm as shown in the figure below. (a) Calculate the final linear velocity of the person, given his mass is 67.5 kg. (b) What is his angular velocity if each arm is 5.00 kg in mass? You may treat his arms as uniform rods of length 0.9 m (measured from the center axis of his body) and the rest of his body as a uniform cylinder of radius 0.170 m. Neglect the effect of the ball on his rotational inertia and on his center of mass, so that it remains in his geometrical center. (Answer is NOT 0.415) (c) Compare the initial and final total kinetic energy. (Answer is NOT 32.92) KEi KEf
Angular Momentum
The momentum of an object is given by multiplying its mass and velocity. Momentum is a property of any object that moves with mass. The only difference between angular momentum and linear momentum is that angular momentum deals with moving or spinning objects. A moving particle's linear momentum can be thought of as a measure of its linear motion. The force is proportional to the rate of change of linear momentum. Angular momentum is always directly proportional to mass. In rotational motion, the concept of angular momentum is often used. Since it is a conserved quantity—the total angular momentum of a closed system remains constant—it is a significant quantity in physics. To understand the concept of angular momentum first we need to understand a rigid body and its movement, a position vector that is used to specify the position of particles in space. A rigid body possesses motion it may be linear or rotational. Rotational motion plays important role in angular momentum.
Moment of a Force
The idea of moments is an important concept in physics. It arises from the fact that distance often plays an important part in the interaction of, or in determining the impact of forces on bodies. Moments are often described by their order [first, second, or higher order] based on the power to which the distance has to be raised to understand the phenomenon. Of particular note are the second-order moment of mass (Moment of Inertia) and moments of force.
Suppose a 0.250-kg ball is thrown at 14.0 m/s to a motionless person standing on ice who catches it with an outstretched arm as shown in the figure below.
(b) What is his
(c) Compare the initial and final total kinetic energy. (Answer is NOT 32.92)
| KEi |
| KEf |
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