Question

determine whether the objects in the following problems have kinetic or potential energy. then choose the correct formula to use!
ke = 1/2 m v²
gpe = mass × gravitational acceleration (9.8 m/s²) × height
gpe = mgh
energy = joules
mass = kilograms
velocity = m/s
gravitational acceleration = 9.8 m/s²

1. you serve a volleyball with a mass of 2.1 kg. the ball leaves your hand with a speed of 31 m/s. the ball has __________ energy. calculate it.
2. a baby carriage is sitting at the top of a hill that is 18 m high. the carriage with the baby has a mass of 1.4 kg. the carriage has __________ energy. calculate it.
3. a car is traveling with a velocity of 30 m/s and has a mass of 1150 kg. the car has __________ energy. calculate it.
4. a cinder block is sitting on a platform 25 m high. it has a mass of 9.5 kg. the block has __________ energy. calculate it.
5. there is a bell at the top of a tower that is 55 m high. the bell has a mass of 19 kg. the bell has __________ energy. calculate it.

Explanation:

Step1: Determine the type of energy

Kinetic energy ($KE=\frac{1}{2}mv^{2}$) is associated with motion. Potential energy ($GPE = mgh$) is associated with height.

• For the volleyball in motion: Kinetic energy.
• For the baby carriage at height: Potential energy.
• For the car in motion: Kinetic energy.
• For the cinder - block at height: Potential energy.
• For the bell at height: Potential energy.

Step2: Calculate the energies

Problem 1: Volleyball (Kinetic energy)

Given \(m = 2.1\space kg\), \(v=21\space m/s\)

$$
LATEXBLOCK0
$$

Problem 2: Baby - carriage (Potential energy)

Given \(m = 1.8\space kg\), \(h = 18\space m\), \(g = 9.8\space m/s^{2}\)

$$
LATEXBLOCK1
$$

Problem 3: Car (Kinetic energy)

Given \(m = 1120\space kg\), \(v = 30\space m/s\)

$$
LATEXBLOCK2
$$

Problem 4: Cinder - block (Potential energy)

Given \(m = 9.5\space kg\), \(h = 25\space m\), \(g = 9.8\space m/s^{2}\)

$$
LATEXBLOCK3
$$

Problem 5: Bell (Potential energy)

Given \(m = 19\space kg\), \(h = 55\space m\), \(g = 9.8\space m/s^{2}\)

$$
LATEXBLOCK4
$$

Answer:

1. Kinetic, \(463.05\space J\)
2. Potential, \(317.52\space J\)
3. Kinetic, \(504000\space J\)
4. Potential, \(2327.5\space J\)
5. Potential, \(10241\space J\)