Question

motion
newtons laws overview
name:
gpb.org/physics - motion
practice problems
work each of the following problems. show all work.

1. which object would have more inertia - a 1,000 kg car or a 150 kg golf cart?
2. what would be harder to accelerate - a 4 kg shot put ball or a 2,000 kg boulder?
3. an object experiences a certain net force that causes a certain acceleration. if the net force on the object is tripled, what happens to the acceleration of the object?
4. a specific net force is applied to an object, and it causes a certain acceleration. if the same net force is applied to a new object with four times the mass, what is the acceleration of the more massive object?

Explanation:

Step1: Recall the concept of inertia

Inertia is directly related to mass. The greater the mass, the greater the inertia.

Step2: Compare masses for question 1

The mass of the car is 1000 kg and the mass of the golf - cart is 150 kg. Since 1000 kg > 150 kg, the 1000 kg car has more inertia.

Step3: Compare masses for question 2

The mass of the shot - put ball is 4 kg and the mass of the boulder is 2000 kg. Since 2000 kg > 4 kg, the 2000 kg boulder is harder to accelerate (because more force is needed to accelerate a more massive object according to Newton's second law $F = ma$).

Step4: Apply Newton's second law for question 3

Newton's second law is $F=ma$, or $a=\frac{F}{m}$. If the mass $m$ is constant and the net force $F$ is tripled (let the original force be $F_1$ and the new force be $F_2 = 3F_1$), and the original acceleration be $a_1=\frac{F_1}{m}$ and the new acceleration be $a_2=\frac{F_2}{m}=\frac{3F_1}{m}=3a_1$. So the acceleration is tripled.

Step5: Apply Newton's second law for question 4

Let the original force be $F$, the original mass be $m_1$ and the original acceleration be $a_1=\frac{F}{m_1}$. The new mass is $m_2 = 4m_1$. The new acceleration $a_2=\frac{F}{m_2}=\frac{F}{4m_1}=\frac{1}{4}a_1$. So the acceleration of the more massive object is one - fourth of the original acceleration.

Answer:

1. The 1000 kg car has more inertia.
2. The 2000 kg boulder is harder to accelerate.
3. The acceleration is tripled.
4. The acceleration of the more massive object is one - fourth of the original acceleration.