Question

At what speed does a 1800 kg compact car have the same kinetic energy as a 15000 kg truck going 21 km/h ? Express your answer in kilometers per hour.

Answer 1

Answer:

v = 60.62 km/h

Explanation:

Kinetic energy

Kinetic energy is that which is due to the movement of bodies and is calculted like this:

K = (1/2)mv² Formula (1)

Where:

K : Kinetic energy (J)

m: mass (kg)

v : speed (m/s)

Data for the truck

m = 15000 kg

v= 21 km/h = 21 *(1000m)/ (3600s)

v= 5.83 m/s

Calculation of the kinetic energy of the truck

We replace data in the formula (1)

K = (1/2)mv²

K = (1/2)(15000)(5.83)²

K = 255208.3 J

Data for the compact car

K = 255208.3 J =  255208.3 (N*m)

m = 1800 kg

Calculation of the speed  of the compact car

We replace data in the formula (1)

K = (1/2)mv²

255208.3 = (1/2)( 1800)(v)²

255208.3 = ( 900)(v)²

v² = 255208.3 / ( 900)

$v= \sqrt{\frac{255208.3}{900} }$

v = 16.84 m/s

1 km = 1000 m

1 h = 3600 s

v = 16.84*(3600/1000)km/h

v = 60.62 km/h