Physics 125A Lecture 17: Lecture 17

After falling from rest from a height of 28 m, a 0.45 kg ball rebounds upward, reaching aheight of 18 m. If the contactbetween ball and ground lasted 2.2 ms, what average force was exerted onthe ball?

An 18-gauge copper wire (diameter 1.02 {\rm mm}) carries a currentwith a current density of 2.00×106 {\rm A/m^{2}}. Copper has 8.5\times 10^{28} free electrons per cubic meter

Part A Calculate the current in the wire (I=A)

Part B Calculate the drift velocity of electrons in the wire. vd=m/s

A spring gun (k = 28 N/m) is used to shoot a 56-g ballhorizontally. Initially
the spring is compressed by 18 cm. The ball loses contact with thespring and leaves the gun when the
spring is still compressed by 12 cm. What is the speed of the ballwhen it hits the ground, 1.4 m
below the spring gun?