A good workout. You overindulged in a delicious dessert, so you plan to work off the extra calories at the gym. To accomplish this, you decide to do a series of arm raises while holding a 5.0 kg weight in one hand. The distance from your elbow to the weight is 35 cm, and in each arm raise you start with your arm horizontal and pivot it until it is vertical. Assume that the weight of your arm is small enough compared with the weight you are lifting that you can ignore it. As is typical, your muscles are 20% efficient in converting the food energy into mechanical energy, with the rest going into heat. If your dessert contained 350 food calories, how many arm raises must you do to work off these calories? Is it realistic to do them all in one session?
A good workout. You overindulged in a delicious dessert, so you plan to work off the extra calories at the gym. To accomplish this, you decide to do a series of arm raises while holding a 5.0 kg weight in one hand. The distance from your elbow to the weight is 35 cm, and in each arm raise you start with your arm horizontal and pivot it until it is vertical. Assume that the weight of your arm is small enough compared with the weight you are lifting that you can ignore it. As is typical, your muscles are 20% efficient in converting the food energy into mechanical energy, with the rest going into heat. If your dessert contained 350 food calories, how many arm raises must you do to work off these calories? Is it realistic to do them all in one session?
A good workout. You overindulged in a delicious dessert, so you plan to work off the extra calories at the gym. To accomplish this, you decide to do a series of arm raises while holding a 5.0 kg weight in one hand. The distance from your elbow to the weight is 35 cm, and in each arm raise you start with your arm horizontal and pivot it until it is vertical. Assume that the weight of your arm is small enough compared with the weight you are lifting that you can ignore it. As is typical, your muscles are 20% efficient in converting the food energy into mechanical energy, with the rest going into heat. If your dessert contained 350 food calories, how many arm raises must you do to work off these calories? Is it realistic to do them all in one session?
A frustrated farmer is trying to move a large rock from his land. The stone has a mass of 9.00×102 kg. By using a piece of board as a lever and a fulcrum the farmer will have a better chance of moving the rock. The farmer places the fulcrum 0.266 m from the rock so that the edge of the board is located directly under the center of the weight of the rock. The farmer can exert a maximum force of 632.0 N. Calculate the minimum total length of board needed to move the stone?
African elephants are the largest land animals. They consume approximately 10% of their body weight in food each day, which for an
adult male, can be 1000 lb. of vegetation! Their diet consists mostly of grasses, bamboo, tree bark, and fruit. They also like to dine on
tree leaves. To reach them, they often stand up on their hind legs and extend their trunks (see the figure). The elephant in the figure is
in equilibrium. The location of the elephant's center of mass is shown, and the axis of rotation has been chosen to correspond to the hip
joint. The forces in the elephant's free-body diagram are shown, and there is a static friction force between the elephant's back feet
and the ground. Use the following information and calculate the magnitude of the tension in the elephant's trunk T (m = 4540 kg, FN
= rfs = 133 cm, rcg = 76.0 cm, r = 229 cm).
Number
+x
Axis of
rotation
Units
60
165
30
W
TTFN
cg
10°
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The slope of the 5.0 KN force F is specified as shown in the figure. Express F as a vector in terms of the unit vectors i and j.
Assume a = 13, b = 6.
Answer: F = (
F
b
i+
j) KN
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