An elevator and counterweight are like atwood’s machine. an elevator, m=100kg, has a counter weight m=90kg connected by a cable over a massless pulley with no friction. the elevator falls, starting from rest, a distance 20.5 m and lands. what the final kinetic energy of the system, in j, just before the elevator lands?

According to social exchange theory, altruistic behaviors benefit the individual who performs them.

Arunner is jogging at a steady 3.6 km/hr. when the runner is 2.9 km from the finish line, a bird begins flying from the runner to the finish line at 14.4 km/hr (4 times as fast as the runner). when the bird reaches the finish line, it turns around and flies back to the runner. even though the bird is a dodo, we will assume that it occupies only one point in space, i.e., a zero-length bird. how far does the bird travel? (b) after this first encounter, the bird then turns around and flies from the runner back to the finish line, turns around again and flies back to the runner. the bird repeats the back and forth trips until the runner reaches the finish line. how far does the bird travel from the beginning? (i.e. include the distance traveled to the first encounter)

If the work required to stretch a spring 3 ft beyond its natural length is 15 ft-lb, how much work is needed to stretch it 27 in. beyond its natural length?