A 3 kg object has two forces acting on it: 10 N to the right and 4 N to the left. What is the magnitude and direction of the object's acceleration?
A4.67 m/s² to the right
B2 m/s² to the right
C3.33 m/s² to the left
D14 m/s² to the right
The net force is 10 N - 4 N = 6 N to the right. By F = ma, a = F_net / m = 6 / 3 = 2 m/s² to the right. The most common error is using the total magnitude of forces (10 + 4 = 14 N) instead of the net force — this tests the misconception of confusing total force with net force.
Question 2 True / False
If no net force acts on a moving object, the object will slow down and eventually stop.
TTrue
FFalse
Answer: False
This is Newton's First Law (the law of inertia), and it is directly connected to the Second Law: when ΣF = 0, then a = 0, meaning the velocity does not change. The object continues at constant velocity. The intuition that things 'naturally stop' comes from everyday experience with friction, which is itself a force.
Question 3 Short Answer
An object has a mass of 5 kg and is accelerating at 3 m/s². If the mass is doubled but the net force stays the same, what happens to the acceleration?
Think about your answer, then reveal below.
Model answer: The acceleration is halved to 1.5 m/s².
From F = ma, if F stays constant and m doubles, then a = F/(2m) = original acceleration / 2. This illustrates the inverse relationship between mass and acceleration: mass is a measure of how much an object resists acceleration.