A net force of 12 N acts on an object of mass 3 kg. What is the magnitude of the object's acceleration?
4 m/s^2
36 m/s^2
9 m/s^2
0.25 m/s^2
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WhyBy Newton's second law, a = F/m = 12 N / 3 kg = 4 m/s^2.
2Multiple choice · Easy
Which of Newton's laws states that an object at rest stays at rest unless acted on by a net external force?
Newton's first law
Newton's second law
Newton's third law
The law of universal gravitation
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WhyNewton's first law (the law of inertia) describes how objects maintain their state of motion when no net force acts.
3Multiple choice · Easy
A book rests on a flat horizontal table. Which force pair best describes the vertical forces acting on the book?
Gravity downward and normal force upward
Normal force downward and gravity upward
Friction upward and tension downward
Applied force forward and gravity backward
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WhyThe downward gravitational force (weight) is balanced by the upward normal force from the table, so the book stays at rest.
4Multiple choice · Easy
On Earth where g = 10 m/s^2, what is the weight of an object with a mass of 5 kg?
50 N
5 N
0.5 N
500 N
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WhyWeight = mg = 5 kg * 10 m/s^2 = 50 N, directed downward toward Earth's center.
5Fill in the blank · Easy
According to Newton's third law, if object A exerts a force on object B, then object B exerts a force on object A that is equal in magnitude and in direction.
Answer:
opposite
WhyNewton's third law states that forces come in action-reaction pairs that are equal in magnitude and opposite in direction.
6Fill in the blank · Easy
The type of friction that acts on an object that is sliding across a surface is called friction.
Answer:
kinetic
WhyKinetic friction acts on objects that are already in motion relative to a surface, opposing the direction of motion.
7Multiple choice · Medium
A 2 kg object experiences two horizontal forces: 10 N to the right and 4 N to the left. What is the object's acceleration?
3 m/s^2 to the right
7 m/s^2 to the right
3 m/s^2 to the left
2 m/s^2 to the right
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WhyNet force = 10 N - 4 N = 6 N to the right; a = F/m = 6 N / 2 kg = 3 m/s^2 to the right.
8Multiple choice · Medium
A box sits on a horizontal floor with a coefficient of static friction of 0.4 and a normal force of 50 N. What is the maximum static friction force before the box begins to slide?
20 N
125 N
50 N
0.4 N
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WhyMaximum static friction = mu_s * N = 0.4 * 50 N = 20 N.
9Multiple choice · Medium
A 4 kg block on a frictionless surface is pulled by a horizontal rope with tension 20 N. What is the block's acceleration?
5 m/s^2
80 m/s^2
0.2 m/s^2
16 m/s^2
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WhyWith no friction, the net horizontal force is the tension, so a = T/m = 20 N / 4 kg = 5 m/s^2.
10Multiple choice · Medium
An elevator accelerates upward at 2 m/s^2 while carrying a 60 kg person. Using g = 10 m/s^2, what is the normal force from the floor on the person?
720 N
600 N
480 N
120 N
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WhyN - mg = ma, so N = m(g + a) = 60 kg * (10 + 2) m/s^2 = 720 N.
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