The forces on a dancer can be measured directly when a dancer performs a jump on a force plate that measures the force between her feet and the ground. A graph of force versus time throughout a vertical jump performed on a force plate is shown in Fig. P4.60. What is happening at 0.4 s ’The dancer is (a) bending her legs so that her body is accelerating downward; (b) pushing her body up with her legs and is almost ready to leave the ground; (c) in the air and at the top of her jump; (d) landing and her feet have just touched the ground.
The forces on a dancer can be measured directly when a dancer performs a jump on a force plate that measures the force between her feet and the ground. A graph of force versus time throughout a vertical jump performed on a force plate is shown in Fig. P4.60. What is happening at 0.4 s ’The dancer is (a) bending her legs so that her body is accelerating downward; (b) pushing her body up with her legs and is almost ready to leave the ground; (c) in the air and at the top of her jump; (d) landing and her feet have just touched the ground.
The forces on a dancer can be measured directly when a dancer performs a jump on a force plate that measures the force between her feet and the ground. A graph of force versus time throughout a vertical jump performed on a force plate is shown in Fig. P4.60. What is happening at 0.4 s ’The dancer is (a) bending her legs so that her body is accelerating downward; (b) pushing her body up with her legs and is almost ready to leave the ground; (c) in the air and at the top of her jump; (d) landing and her feet have just touched the ground.
An inventive child wants to reach an apple in a tree without climbing the tree. Sitting in a chair connected to a rope that passes over a frictionless pulley (Fig. P4.81), the child pulls on the loose end of the rope with such a force that the spring scale reads 250 N. The child’s true weight is 320 N, and the chair weighs 160 N. The child’s feet are not touching the ground. (a) Show that the acceleration of the system is upward, and find its magnitude. (b) Find the force the child exerts on the chair.
A setup similar
to the one shown in Figure
P4.53 is often used in hospi-
tals to support and apply a
traction force to an injured
leg. (a) Determine the force
of tension in the rope sup-
porting the leg. (b) What is
the traction force exerted
8.00 kg
Figure P4.53
on the leg? Assume the traction force is horizontal.
A woman at an airport is towing her 15.0 kg suitcase at constant speed by pulling on a strap at an angle θ above the horizontal (see figure). She pulls on the strap with a 28.5 N force, and the friction force on the suitcase is 20.0 N.
(a) If the woman still pulls on the strap with a 28.5 N force but wishes to accelerate the suitcase at a rate of 0.500 m/s2, at what angle (in degrees) must she pull on the strap? Assume that the rolling friction is independent of the angle of the strap.
(b)What is the maximum acceleration of the suitcase if the woman can exert a maximum force of 28.5 N? (Enter the magnitude in m/s2.)
Chapter 4 Solutions
University Physics with Modern Physics (14th Edition)
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