Kinetic energy
Answers are for parents and teachers.
1
m = 6 kg, υ = 3 m/s. E_k (J)?
27
2
E_k = 90 J, m = 5 kg. υ (m/s)?
6
3
A 2 kg body speeds up from 5 to 10 m/s. Work done on it (J)?
75
4
Why are there speed limits on roads?
Kinetic energy grows with the square of speed, so crashes are worse and braking distance longer.
5
Why wear a helmet and limit speed on a bike?
In a fall the kinetic energy is large; a helmet softens the blow.