Question

A projectile with a mass of 9.40 g is travelling at a speed of 1.14 km/s.

(a) Determine the kinetic energy of the projectile in kilojoules.
kJ

(b) Determine the kinetic energy of the projectile in kilojoules, if its speed is reduced by a factor of two.
kJ

(c) Determine the kinetic energy of the projectile in kilojoules, if its original speed is increased by a factor of three.
kJ

Answer 1

here,

mass of projectile , m = 9.4 g = 0.0094 kg

speed , v = 1.14 km/s = 1140 m/s

a)

the kinetic energy of the projectile , KE = 0.5 * m * v^2

KE = 0.5 * 0.0094 * 1140^2 J = 6108 J

KE = 6.11 KJ

b)

kinetic energy is proportional to the square of speed

when the speed is reduced by a factor of two

the kinetic energy is reduced by a factor of four(2^2)

so, the new kinetic energy, KEb = KE/4 = 1.53 KJ

c)

kinetic energy is proportional to the square of speed

when the speed is increased by a factor of three

the kinetic energy is increased by a factor of 9(3^2)

so, the new kinetic energy, KEc = KE * 9 = 54.97 KJ