Question

The mass of cyclist together with the bike is 90 kg. Calculate the increase in kinetic energy if the speed increases from 60 km/h to 12 km/h.
Concept of Physics - 1 , HC VERMA , Chapter " Work and Energy"

Answer 1

Hello Dear.

Given

Mass of the cyclist together with the bike(m) = 90 kg.
Initial Speed(u) = 60 km/hr.
= 60 × 5/18  [Changing into m/s.]
= 5/3 m/s.

Final Speed(v) = 12 km/hr.
= 12 × 5/18  [Changing into m/s.]
= 10/3 m/s.

Increases in Kinetic Energy = 1/2 × m(v² - u²)

= 1/2 × 90 × [(10/3)² - (5/3)²]
= 45 × [100/9 - 25/9]
= 45 × [75/9]
= 5 × 75
= 375 J.


Hence, the increases in the kinetic energy of the cyclist is 375 J.


Hope it helps.

Answer 2

HEY!!

_____________________________

▶Total mass of the system (cyclist and bike), M = mc+mb = 90 kg

▶Initial velocity of the system, u=6.0 km/h= 1.666 m/sec

▶Final velocity of the system, ν=12 km/h = 3.333 m/sec

▶From work-energy theorem, we have:-

▶Increase in K.E.= 1/2 Mν^2−1/2mu^2

▶1/2 90×(3.333)^2−1/2 ×90×(1.66)^2

✔499.4−124.6

✔374.8

✔✔375 J