A boy with mass 50 kg running at 5m/s jumps on to a 20 kg trolley travelling in the same direction at 1.5 m/s. What is their common velocity?

Explanation:

Boy information

Mass = 50kg

Velocity = 5m/s

Trolley information

Mass = 20 kg

Velocity = 1.5 m/s

so using conservation law of momentum

MV + mv = ( M + m ) v'

50*5 + 20*1.5 = ( 50 + 20 ) v'

250 + 30 = 70 v'

280 = 70 v'

so v' = 4m/s which is their common velocity.

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.