Question

At what speed does a 1500 kg compact car have the same kinetic energy as a 18000 kgkg truck going 21 km/hr km/hr

Answer 1

Answer:

speed = 72.75km/hr

Explanation:

Let us first determine the Kinetic energy (KE) of the 18000kg truck

$KE = \frac{1}{2} mv^2\\where:\\m = mass = 18000\\v = velocity = 21km/hr\\\therefore KE = \frac{1}{2} \times 18000 \times (21)^2\\= 9000 \times 441\\KE = 3,969,000\ Joules\\= 3,969\ KJ$

Next we will substitute this value of kinetic energy into the KE equation for the 1500kg compact car

$KE = \frac{1}{2} mv^2\\3969000 = \frac{1}{2} \times 1500 \times v^2\\3969000 = 750 \times v^2\\v^2 = \frac{3969000}{750} = 5292\\v = \sqrt{5292} \\v = 72.75km/hr$