Question

10. A small object of mass m, on the end of a light cord, is held horizontally at a distance r from a fixed support as shown. The object is then released. What is the tension in the cord when the object is at the lowest point of its swing? 11. A wooden brick slides on a horizontal frictionless floor with a constant velocity v. On the brick's path there is a 50 cm long rough area with a friction coefficient of p=0.4. Find the minimal speed required for the brick to make it through the rough area. 12. A 25-g ball is released from rest 80 m above the surface of the Earth. During the fall the total thermal energy of the ball and air increases by 15 3. Just before it hits the surface its Kinetic energy is:

Answer 1

10.

h = height above the lowest point = r

Using conservation of energy :

Potential energy at the top = Kinetic energy at lowest point

mgh = (0.5) m V²

mgr = (0.5) m V²

V² = 2gr                      eq-1

at the lowet point , Force equation is given as

T - mg = mv²/r

T - mg = 2mg

T = 3mg