**Chapter 9 Practice 2**

A 5.0 kg mass hanging from a spring scale is slowly lowered onto a vertical spring, as shown. The scale reads in newtons.

A. What does the spring scale read just before the mass touches the lower spring?

B. The scale reads 20 N when the lower spring has been compressed 2.0 cm. What is the value of the spring constant for the lower spring?

C. At what compression length will the scale read zero?

49 N

1450 N/m

3.38 cm

A horizontal spring with spring constant 85 N/m extends outward from a wall just above floor level. A 4.5 kg box sliding across a frictionless floor hits the end of the spring and compresses it 3.5 cm before the spring expands and shoots the box back out. How fast was the box going when it hit the spring?

.15 m/s

An 8.3 kg crate is pulled 5.0 m up a 30 incline by a rope angled 19 above the incline. The tension in the rope is 120 N and the crate's coefficient of kinetic friction on the incline is 0.26.

What is the work done by tension, gravity and the normal force? What is the thermal energy change of the system?

o

o

570 -200 0 41 J

How fast is it going?

8.9 m/s

Two identical horizontal springs are attached to opposite sides of a box that sits on a frictionless table. The outer ends of the springs are clamped while the springs are at their equilibrium lengths. Then a 2.6 N force applied to the box, parallel to the springs, compresses one spring by 3.5 cm while stretching the other by the same amount.

37 N/m

A 50 g rock is placed in a slingshot and the rubber band is stretched. The magnitude of the force of the rubber band on the rock is shown by the graph. The rubber band is stretched 30 cm and then released.

What is the speed of the rock?

19 m/s

When you ride a bicycle at constant speed, nearly all the energy you expend goes into the work you do against the drag force of the air. Model a cyclist as having cross-section area 0.46 m^2 and, because the human body is not aerodynamically shaped, a drag coefficient of 0.90.

What is the cyclist's power output while riding at a steady 7.3 m/s (16 mph)?

100 W

A farmer uses a tractor to pull a 190 kg bale of hay up a 15 incline to the barn at a steady 5.0 km/h. The coefficient of kinetic friction between the bale and the ramp is 0.45.

o

What is the tractors power output?

1800 W

A 95 kg firefighter needs to climb the stairs of a 30-m-tall building while carrying a 45 kg backpack filled with gears. How much power does he need to reach the top in 60 s?

690 W

"Can you explain hookes law?"

"I'm still having trouble finding the angle for vector multiplication. Could we go over it in class again"

"What is a restoring force?"

"Could you explain more about the concept of dissipative forces?"