1. A 2-kg object is moving at 3 m/s. A 4-N force is applied in the direction of motion and them removed after the object has traveled an additional 5 m. The work done by this force is:

A) 12 J     B) 15 J       C) 18 J      D) 20 J       E) 38 J

4-N force is applied in the direction of motion so the angle between the force and displacement is 0. W = |F| |d| cos0 = 4 *5 =20

2. A 2-kg particle on the end of an ideal spring with the spring constant k = 200N/m is pulled out 0.5 m and released from rest. When it passes the equilibrium point its speed is:

A) 0      B) 0.05 m/s     C) 5 m/s       D) 10 m/s         E) 100 m/s

Initial velocity is 0. Final velocity (when it passes the equilibrium point) is v. D K = 1/2mv² - 0 = 1/2mv²
D K = Work done by the spring = 1/2kx² 1/2mv² = 1/2kx² v = x Ö k/m = 0.5 * 10 = 5
 
 

3. An 1200-kg escalator is used to move 20 people (60 kg each) per minute from the first floor of a department store to the second floor, 5 m above. The power required is approximately:

A) 1,000 W       B) 2,000 W        C) 10,000 W        D) 20,000 W       E) 60,000 W

Work > (1200 + 20 * 60) * 9.8 * 5 W (escalator used to have its own mass) P = W/t = 120,000/1min = 120,000/60 = 2,000 W