Mixing Units and Kinetic Energy Calculations 1

Question: If a car has a mass of 900 kg and is driving at 60 km / hr, what is its kinetic energy?

Answer:

Step 1: Analyze the question to determine what information is provided

• The mass of the car
  
• The speed of the car
  
  . These are not the units we want so before we continue we must convert to m / s. We do this by multiplying by one:
• 
• Now we need to change from hours to seconds so we repeat our procedure:
• 
• and so the speed in the units we want is
  

Step 2: Analyze the question to determine what is being asked

• We are asked to find the kinetic energy

Step 3: Substitute and calculate

We know we need the mass and speed to work out E _k and we are given both of these quantities. We thus simply substitute them into the equation for E _k: