(a) Calculate the kinetic energy, in joules, of a 15-g bullet moving at $120 \mathrm{~m} / \mathrm{s}$. (b) Convert this energy to calories. (c) When the bullet is stopped by a bulletproof vest, which form of energy does the kinetic energy of the bullet convert to?

Short Answer

Expert verified
The bullet has a kinetic energy of 108 Joules or approximately 25.8 calories. When it is stopped by a bulletproof vest, the kinetic energy mainly converts to heat energy.

Step by step solution

01

Calculate the Kinetic Energy

First, we need to find the kinetic energy (KE) of the bullet. We have the mass in grams (15g), but we need it to be in kilograms for the calculation. To convert mass m from grams to kilograms, divide by 1000: m = 15g / 1000 = 0.015 kg Now we can calculate the kinetic energy using the formula: KE = (1/2)mv^2 Plug in values for mass (m) and velocity (v): KE = (1/2)(0.015 kg)(120 m/s)^2
02

Convert Joules to Calories

Now, we can find the value of the kinetic energy (KE) in Joules: KE = 108 Joules To convert this to calories, we can use the following formula: Calories = Joules / 4.184 Calories = 108 J / 4.184
03

Energy Conversion When Bullet is Stopped by a Bulletproof Vest

When the bullet is stopped by a bulletproof vest, its kinetic energy is converted to another form of energy, mainly heat energy due to the friction between the bullet and the vest's material. Some deformation of the bullet and vest material can also lead to a small amount of other internal energy being generated.
04

Summary

The kinetic energy of the bullet is 108 Joules or approximately 25.8 calories. When the bullet is stopped by a bulletproof vest, the main form of energy it is converted to is heat energy.

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