Question

1. fill in the blanks: potential energy is shown in the picture 4. in this situation, what type of energy is there? 2. identify the types of energy (including at least 4 forms of energy) for a rock held above the ground then dropped, i.e. chemical - stored, heat, gravity - potential, kinetic, light - radiation, nuclear - radioactive. 3. if you push a car with a force of 100 n and it moves 6 m, how much work energy did you do? 4. a 3 kg rock is held 2 m above the ground. a. what is the force of gravity on the rock? b. if you pick the rock up and hold it 3 m above the ground, how much work did you do? c. it is then dropped to the ground with a bang!!! how much heat energy is produced by the time the sound and vibrations have ended? 5. now you throw the 3 kg rock with a velocity of 4 m/s, how much kinetic energy do you give the rock?

Explanation:

Step1: Calculate work in question 3

Use work - formula $W = F\times d$. Given $F = 100\ N$ and $d = 6\ m$.
$W=100\times6 = 600\ J$

Step2: Calculate gravitational force in 4a

Use formula $F = mg$. Given $m = 3\ kg$ and $g= 9.8\ m/s^{2}$.
$F = 3\times9.8=29.4\ N$

Step3: Calculate work in 4b

The force needed to lift the rock is equal to its weight $F = mg = 29.4\ N$. The displacement $d=(3 - 2)\ m = 1\ m$. Use $W = F\times d$.
$W=29.4\times1 = 29.4\ J$

Step4: Calculate heat energy in 4c

The initial potential energy of the rock when it is 3 m above the ground is $U = mgh=3\times9.8\times3 = 88.2\ J$. When it hits the ground and all sound and vibrations end, all of its initial potential energy is converted into heat energy. So the heat energy $Q = 88.2\ J$

Step5: Calculate kinetic energy in question 5

Use kinetic - energy formula $K=\frac{1}{2}mv^{2}$. Given $m = 3\ kg$ and $v = 4\ m/s$.
$K=\frac{1}{2}\times3\times4^{2}=\frac{1}{2}\times3\times16 = 24\ J$

Answer:

1. $600\ J$

4a. $29.4\ N$
4b. $29.4\ J$
4c. $88.2\ J$

1. $24\ J$