Select the best dated evidence that humans have been on earth for over four million years from the choices provided. a. a fossil nicknamed lucy was found in east africa. b. a specimen nicknamed ardi was found in east africa. c. artifacts from the stone age were discovered in east africa. d. evidence from the last ice age was found in east africa.

Aplayground slide is 8.80 ft long and makes an angle of 25.0° with the horizontal. a 63.0-kg child, initially at the top, slides all the way down to the bottom of the slide. (a) choosing the bottom of the slide as the reference configuration, what is the system's potential energy when the child is at the top and at the bottom of the slide? what is the change in potential energy as the child slides from the top to the bottom of the slide? (include the sign of the value in your answer.)