Physics 104
Lab -7 Physics Problem Solving – Work and Energy
Name:
Date:
Partner:
Instruction: Pair up with one partner and work on these questions for one hour. Your
goal should be to show all the work, so that someone else can understand it. Your
instructor will give you further instructions after one hour.
1. A person doing a chin-up weighs 685 N exclusive of the arms. During the first
16.0 cm of the lift, each arm exerts an upward force of 355 N on the torso. If the
upward movement starts from rest, what is the person’s speed at the point?
(Answer: 0.338 m/s)
2. Water flows over a section of Niagara Fall at the rate of 1.26 x 106 kg/s and fall
48 m. How much power is generated by the falling water? (Answer: 5930 MW).
3. A 5N force acts on an object for a distance of 4 m and then the force decreases at
a constant rate until the object has moved another 2 m where the force is zero.
What is the total work done by the variable force? (Answer: 25 J).
4. The launching mechanism of a toy gun consists of a spring of unknown spring
constant, as shown in Figure P5.33a. If its spring is compressed a distance of
0.160 m and the gun fired vertically as shown, the gun can launch a 19.0 g
projectile to a maximum height of 26.0 m above the starting
point of the projectile. Figure P5.33
a. Neglecting all resistive forces, determine the spring
constant. (Answer: 378 N/m)
b. Neglecting all resistive forces, determine the speed of the
projectile as it moves through the equilibrium position of
the spring (where x = 0), as shown in Figure 5.33b. (Answer: 25.86 m/s).
5.
In the dangerous “sport” of bungee-jumping, a daring student jumps from a
balloon with a specially designed elastic cord attached to his waist. (See text P77).
The un-stretched length of the cord is 23.0 m, the student weighs 675 N, and the
balloon is 36.0 m above the surface of a river below. Calculate the required force
constant of the cord if the student is to stop safely 5.0 m above the
river.(Answer:654 N/m)