Multiple Choice
When switch S in the figure is closed at time , which of the following best describes the motion of a block of mass attached to a horizontal frictionless surface and pulled by a constant force ?
6. Intro to Forces (Dynamics)
Newton's First & Second Laws
Multiple Choice
According to Newton's first law, if the net force on an object is zero (), which statement must be true about its motion?
A
It can have a nonzero acceleration as long as its speed is constant.
B
Its acceleration is zero, so it remains at rest or moves with constant velocity.
C
It must be at rest.
D
It must be moving with increasing speed.
Verified step by step guidance1
Recall Newton's first law, which states that if the net force on an object is zero (\(F_{net} = 0\)), the object will not experience any change in its motion.
Understand that acceleration is caused by a net force according to Newton's second law: \(F_{net} = m \times a\), where \(m\) is mass and \(a\) is acceleration.
Since \(F_{net} = 0\), substitute into the equation to get \(0 = m \times a\), which implies that the acceleration \(a\) must be zero.
With zero acceleration, the object cannot change its velocity, meaning it either remains at rest or continues to move at a constant velocity (constant speed and direction).
Therefore, the correct statement is that the object's acceleration is zero, so it remains at rest or moves with constant velocity.
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