* Elena, a black belt in tae kwon do, is experienced in breaking boards with her fist. A high-speed video indicates that her forearm is moving with a rotational speed of 40 rad/s when it reaches the board. The board breaks in 0.0040 s and her arm is moving at 20 rad/s just after breaking the board Her fist is 0.32 m from her elbow joint and the rotational inertia of her forearm is 0 .050 kg m 2 . Determine the average force that the board exerts on her fist while breaking the board (equal in magnitude to the force that her fist exerts on the board) ignore the gravitational force that Earth exerts on her arm and the force that her triceps muscle exerts on her arm during the break.
* Elena, a black belt in tae kwon do, is experienced in breaking boards with her fist. A high-speed video indicates that her forearm is moving with a rotational speed of 40 rad/s when it reaches the board. The board breaks in 0.0040 s and her arm is moving at 20 rad/s just after breaking the board Her fist is 0.32 m from her elbow joint and the rotational inertia of her forearm is 0 .050 kg m 2 . Determine the average force that the board exerts on her fist while breaking the board (equal in magnitude to the force that her fist exerts on the board) ignore the gravitational force that Earth exerts on her arm and the force that her triceps muscle exerts on her arm during the break.
* Elena, a black belt in tae kwon do, is experienced in breaking boards with her fist. A high-speed video indicates that her forearm is moving with a rotational speed of 40 rad/s when it reaches the board. The board breaks in 0.0040 s and her arm is moving at 20 rad/s just after breaking the board Her fist is 0.32 m from her elbow joint and the rotational inertia of her forearm is
0
.050 kg m
2
. Determine the average force that the board exerts on her fist while breaking the board (equal in magnitude to the force that her fist exerts on the board) ignore the gravitational force that Earth exerts on her arm and the force that her triceps muscle exerts on her arm during the break.
What is the current, in amps, across a conductor that has a resistance of10 Ω and a voltage of 20 V?
2. A conductor draws a current of 100 A and a resistance of 5 Ω. What is thevoltageacross the conductor?
3. What is the resistance, in ohm’s, of a conductor that has a voltage of 80 kVand acurrent of 200 mA?
4. An x-ray imaging system that draws a current of 90 A is supplied with 220V. What is the power consumed?
5. An x-ray is produced using 800 mA and 100 kV. What is the powerconsumed in kilowatts?
Part C
Find the height yi
from which the rock was launched.
Express your answer in meters to three significant figures.
Learning Goal:
To practice Problem-Solving Strategy 4.1 for projectile motion problems.
A rock thrown with speed 12.0 m/s and launch angle 30.0 ∘ (above the horizontal) travels a horizontal distance of d = 19.0 m before hitting the ground. From what height was the rock thrown? Use the value g = 9.800 m/s2 for the free-fall acceleration.
PROBLEM-SOLVING STRATEGY 4.1 Projectile motion problems
MODEL: Is it reasonable to ignore air resistance? If so, use the projectile motion model.
VISUALIZE: Establish a coordinate system with the x-axis horizontal and the y-axis vertical. Define symbols and identify what the problem is trying to find. For a launch at angle θ, the initial velocity components are vix=v0cosθ and viy=v0sinθ.
SOLVE: The acceleration is known: ax=0 and ay=−g. Thus, the problem becomes one of…
Chapter 9 Solutions
College Physics: Explore And Apply, Volume 2 (2nd Edition)
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