- #1

NguyenAdam

- 1

- 0

Kinetic Energy = 1/2 mv^2

Potential Energy = mgh

Work = Fd

**KE(initial) + PE(initial) = KE(final) + PE(final)**

The height above the ground of a child on a swing varies from 50 cm at the lowest point to 200 cm at the highest point. The maximum speed of the child is?

A. about 5.4 m/s

B. about 7.7 m/s

C. about 29 m/s

D. dependent on the child's mass

The answer for this question is A, and I do not understand how they got it.

I also have one more question.

The 2.0-kg head of an ax is moving at 60 m/s when it strikes the log. If the blade of the ax penetrates 20 mm into the log, the average force it exerts is

A. 3 kN

B. 90 kN

C. 72 kN

D. 180 kN

The answer is 180 kN.

I have no idea where to start for these problems. Help would really be appreciated!