Question

A 900-kg compact car moving at 60 mi/hr has approximately 320 000 Joules of kinetic energy. Estimate its new kinetic energy if it is moving at 30 mi/hr.

Answer 1

Answer

80,923 Joules

Explanation

You know that the mass =900 kg

Vi = 30 mi/ hr * 1 hr / 3600 sec * 1609.34 meter / mi

Vi= 13.41 meters per second

Use equation KE = .5 m v^2

KE f = .5 (900)(13.41)^2 =80,923 Joules

Answer 2

Answer:

It's new kinetic energy is 80000 J

Explanation:

Given,

Mass = 900 kg ,Speed = 60 m/hr

We know,

Kinetic energy = 1/2 mass x Square of velocity

$Here \: speed \: reduced \: by \: factor \: of \: 2 \: ( From \: 60 m/ hr \: to \: 30 m/hr)$

So, KE means kinetic energy will be reduced by a factor of 4 [Because we know that KE is directly related square of the speed]

Thus new kinetic Energy is

$\frac{320000 \: j}{4} = 80000 \: j$