Question

In which of these situations, is mechanical energy being conserved? (Neglect, air resistance, friction, and breaking) Check all that apply.
Child on a swing


Pendulum


Bow and Arrow


Roller Coaster

Question 2
As an object falls to the ground, its potential energy is being converted to kinetic energy.


True
False
Question 3
The energy that an object has stored due to its position or shape is called:

kinetic energy


potential energy


chemical energy


electrical energy

Question 4
Calculate the potential energy stored in a 10 kg block, 5 meters above the ground.


490 J


50 J


490 N


50 N

Question 5
An elevator weighs 1500 Newtons. Calculate how much potential energy it has when it is lived 500 meters in the air.


75,000 J


750 J


7,500,000 J


750,000 J

Answer 1

1. mechanical energy is conserved in all the listed situations
2. true
3. potential energy
4. 490 J
5. 750,000 J

EXPLANATION

1. sum of kinetic energy (KE) and potential energy (PE) is known as          mechanical energy

• kinetic energy is the motion of an object

• potential energy is the position of an object

there is kinetic energy and other energies in the listed situation.

2. since the height decreases due to the fall, the potential energy also decreases but the speed increases and kinetic energy simultaneously increases so the potential energy is converted to kinetic energy.

3.the energy consumed by an object due to its position is known as potential energy

4. potential energy

        PE = m g h

      m = 10 kg mass of the object

      g = 9.8 m/s^2 acceleration of gravity

      h= 5 m height of the object from ground

substituting every value in the formula

   PE = (10)(9.8)(5)

   PE= 490 J

5. potential energy

      PE = m g h

but given is the weight and the height of the elevator

      W= 1500 N

       h= 500 m

but weight of the object is equal to the product of acceleration of gravity and mass of the elevator  

so,     W = mg

so we can rewrite the formula as PE = Wh

PE = (1500)(500)

PE= 750,000 J