Let’s solve the problems step by step. We’ll use the formulas given:
Kinetic Energy (KE) = ½ × m × v²
→ where *m* is mass in kg, and *v* is velocity in m/s
Potential Energy (PE) = m × g × h
→ where *m* is mass in kg, *g* is gravity (we’ll use 9.8 m/s²), and *h* is height in meters
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Problem 15:
> You are a catcher with a mass of 7.2 kg. The ball leaves your hand with a speed of 40 m/s. The ball has a mass of 0.15 kg. What is its kinetic energy? Calculate it and show your work!
Wait — let’s read carefully. It says “you are a catcher with a mass of 7.2 kg” — but then asks for
the ball’s kinetic energy. So we ignore the catcher’s mass. We only care about the ball.
Ball’s mass (*m*) = 0.15 kg
Ball’s speed (*v*) = 40 m/s
Use KE formula:
KE = ½ × m × v²
= 0.5 × 0.15 × (40)²
First, calculate 40 squared:
40 × 40 = 1600
Now multiply:
0.5 × 0.15 = 0.075
Then: 0.075 × 1600 = ?
Let’s do that:
0.075 × 1600
= 75/1000 × 1600
= (75 × 1600) / 1000
= 120,000 / 1000
= 120
✔ So, KE =
120 Joules
*(Note: The example in the image shows PE = 300 J for a different problem — don’t confuse them. This one is KE.)*
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Problem 16:
> A baby carriage is sitting at the top of a hill that is 21 m high. The carriage with the baby has a mass of 1.5 kg. The carriage has what kind of energy? How much? Calculate it and show your work!
It’s at the top of a hill → not moving → so it has
potential energy, not kinetic.
Mass (*m*) = 1.5 kg
Height (*h*) = 21 m
Gravity (*g*) = 9.8 m/s²
PE = m × g × h
= 1.5 × 9.8 × 21
Let’s break it down:
First, 1.5 × 9.8
= (1 × 9.8) + (0.5 × 9.8)
= 9.8 + 4.9 = 14.7
Now, 14.7 × 21
We can do: 14.7 × 20 + 14.7 × 1
= 294 + 14.7 = 308.7
✔ So, PE =
308.7 Joules
*(The image shows an example calculation: PE = 1.5 × 9.8 × 21 = 308.7 J — which matches our answer!)*
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Final Answer:
Problem 15: 120 J
Problem 16: 308.7 J
Parent Tip: Review the logic above to help your child master the concept of kinetic and potential energy worksheet answers.
