Question

A projectile must have 150 kJ of kinetic energy to break through a city wall. Which of the following projectiles will break through the wall?
A. Mass = 100 kg; speed = 55 m/s
B. Mass = 150 kg; speed = 42 m/s
C. Mass = 200 kg; speed = 36 m/s
D. All of the above

Answer 1

Answer:

A. Mass = 100 kg; speed = 55 m/s

Explanation:

The kinetic energy of an object is the energy that an object possessed due to its motion.

It is given by:

$KE=\frac{1}{2}mv^2$

where

m is the mass of the object

v is its speed

Here we have to compare the kinetic energy of the three projectiles.

For projectile A:

A. Mass = 100 kg; speed = 55 m/s

So its KE is

$KE=\frac{1}{2}(100)(55)^2=151,250 J = 151.3 kJ$

For projectile B:

B. Mass = 150 kg; speed = 42 m/s

So its KE is

$KE=\frac{1}{2}(150)(42)^2=132,300 J=132.3 kJ$

For projectile C:

C. Mass = 200 kg; speed = 36 m/s

So its KE is:

$KE=\frac{1}{2}(200)(36)^2=129,600 J=129.6 kJ$

So, only projectile A has enough energy (150 kJ) to break the wall.