Question

Your friend is on rollerblades holding a pendulum. You gently push her forward and let go. You observe that the pendulum first swings in the opposite direction (backward) and then returns to the vertical orientation as she coasts forward.

Part A
Choose the correct force diagram of the pendulum bob (in inertial reference flame) as your friend is being pushed. y-direction is the vertical direction.

Answer 1

The correct force diagram for a pendulum bob as a friend on rollerblades is pushed forward would include gravitational force acting downward and tension in the pendulum's string acting upwards and slightly backwards.

Step-by-step explanation:

Force Diagram for a Pendulum on Rollerblades

When your friend on rollerblades is holding a pendulum and you gently push her forward, the correct force diagram of the pendulum bob in an inertial reference frame should include the following forces:

• Gravitational force (weight) acting downward, towards the center of Earth.
• Tension in the string of the pendulum, acting upwards and slightly backwards when the person is being pushed. This is because the pendulum is momentarily lagging behind as the person starts moving forward.

Therefore, as your friend is pushed forward and starts moving, the pendulum bob experiences a backward movement due to its inertia. The force of gravity and the tension in the string combine to create a restoring force that eventually brings the pendulum back to its vertical orientation.

The yoyo examples provided (a and b) discuss the centripetal force but are not directly related to the pendulum scenario. Similarly, the sled examples and merry-go-round scenarios provide insight into forces acting on objects in different contexts but do not represent the exact forces on the pendulum held by a person on rollerblades.

Answer 2

It would be using Newton's First Law. Newton's First Law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. It may be seen as a statement about inertia, that objects will remain in their state of motion unless a force acts to change the motion.