Question

if an object is moving, which of the following must be true? choose all that apply.
the object has ke.
the object has momentum.
the object has pe.
the object has a net force acting on it.
the object has a constant velocity.
the object is accelerating.
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1. -/1 points

if a figure skating is spinning around with her arms outstretched, why will she spin faster if she brings her arms in?
by bringing in her arms she is reducing the air drag on her and hence, she spins faster.
momentum is always conserved. by bringing her arms in she is decreasing her mass. with less mass, in order to keep her
angular momentum is always conserved. by bringing her arms in she is decreasing her radius. in order to keep her angular
energy is always conserved. by bringing her arms in she is decreasing her pe. to keep her total energy constant her ke must

Explanation:

Step1: Analyze Kinetic Energy (KE)

Kinetic energy formula is \(KE=\frac{1}{2}mv^{2}\). If an object is moving (\(v
eq0\)), then \(KE> 0\).

Step2: Analyze Momentum

Momentum formula is \(p = mv\). If \(v
eq0\), then \(p
eq0\).

Step3: Analyze Potential Energy (PE)

Potential energy (\(PE\)) depends on position (e.g., \(PE = mgh\) for gravitational potential energy). Just because an object is moving does not mean it has potential energy. For example, a moving object on the ground (\(h = 0\)) has no gravitational \(PE\).

Step4: Analyze Net Force

An object can move with constant velocity (\(a=0\)). From Newton's second law \(F_{net}=ma\), if \(a = 0\), then \(F_{net}=0\).

Step5: Analyze Constant Velocity

An object can be accelerating (\(a
eq0\)) and still be moving. So, it is not necessary to have constant velocity.

Step6: Analyze Acceleration

An object can move with \(v
eq0\) and \(a = 0\) (constant velocity motion).

For the second question:

Step1: Recall Angular Momentum Conservation

The formula for angular momentum is \(L = I\omega\), where \(I\) is the moment of inertia and \(\omega\) is the angular velocity. Angular momentum \(L\) is conserved (\(L_{initial}=L_{final}\)) in the absence of external torques.

Step2: Analyze Moment of Inertia Change

The moment of inertia for a distributed - mass object (like a skater) is \(I=\sum mr^{2}\). When the skater brings her arms in, she is decreasing the radius \(r\) of the mass distribution. So, \(I\) decreases (\(I_{final}

Step3: Analyze Angular Velocity Change

Since \(L = I\omega\) and \(L_{initial}=L_{final}\), if \(I\) decreases (\(I_{final}\omega_{initial}\)) to keep \(L\) constant.

Answer:

For the first part:

• The object has KE.
• The object has momentum.

For the second part: Angular momentum is always conserved. By bringing her arms in she is decreasing her radius. In order to keep her angular momentum constant, her angular velocity must increase.