PHY 1151

Chapter 7; Work and Kinetic Energy

 

| ToC, Chapter 7 | Course Calendar |

 

D7.1 How much work is done by gravity on a skier weighing 600 N who slides 500 m down a hill (measured along the hill) which makes an angle of 30° with the horizontal as sketched in the figure?

D7.2 In playing shuffleboard, a long wooden stick is used to give a push to a 0.3 kg puck and cause it to move across the floor. A player pushes with a force of 25 N along the stick, inclined 40° to the ground. The coefficient of friction between puck and floor is 0.10.

a) How much work is done on the puck by the stick as it moves a distance of 0.7 m?
b) What will be the puck's speed after it has moved that 0.7 m, assuming it started at rest?
c) From there the puck leaves the stick and slides across the floor. How far will it slide?
D7.3 An electric bill lists 1284 kW-h as the energy used for a month. If the charge is 11.5 cents per kW-h, what is the total bill? How many joules of energy were used that month?
D7.4 The output of a common student laboratory laser is about 250 milliwatts. How much energy is delivered in one hour?
D7.5 The power of a boat’s motor at a speed of 40.0 km/h is 22.0 kW. If the power is 15% greater while pulling a skier at the same speed, what is the tension in the tow rope?

P = F v (assuming F and v are parallel)

D7.6 What is the kinetic energy of a 1750 kg car traveling at 80 km/h?

KE = (1/2) m v2

D7.7 Below are data for eight air track gliders with different masses and speeds. Calculate the values of their kinetic energies.
mass (kg)
speed (m/s)
A
0.225 kg
0.85 m/s
B
0.225
0.90
C
0.250
0.35
D
0.250
0.50
E
0.267
0.65
F
0.315
0.82
G
0.450
0.45
H
0.450
0.52
KE = (1/2) m v2

D7.8 The pilot of the first successful human-powered, heavier-than-air flight could generate an average of 0.32 kW (0.43 hp) during the flight. The aircraft covered 2.4 km at an average speed of 4.1 m/s. How much energy was expended during the flight?

 

| ToC, Chapter 7 | Course Calendar |

 

(c) 2005, Doug Davis; all rights reserved.