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.
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.)
4.57 CP Two boxes, A and B, are connected to
each end of a light vertical rope, as shown in
Fig. P4.57. A constant upward force F =
80.0 N is applied to box A. Starting from rest,
box B descends 12.0 m in 4.00 s. The tension in
the rope connecting the two boxes is 36.0 N.
(a) What is the mass of box B? (b) What is the
mass of box A?
23. A 1.00 × 10³-N crate is being pushed across a level floor at a
constant speed by a force F of 3.00 × 10² N at an angle of 20.0°
below the horizontal, as shown in Figure P4.23a. (a) What is the
coefficient of kinetic friction between the crate and the floor?
(b) If the 3.00 × 10-N force is instead pulling the block at an
angle of 20.0° above the horizontal, as shown in Figure P4.23b,
what will be the acceleration of the crate? Assume that the coef
ficient of friction is the same as that found in part (a).
31.
Chapter 4 Solutions
University Physics with Modern Physics, Volume 2 (Chs. 21-37); Mastering Physics with Pearson eText -- ValuePack Access Card (14th Edition)
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