Answered: A5 kg object under the influence of a…

A5 kg object under the influence of a varying force F as shown in figure. If the object start from rest at x 0 then its speed at x=8 m is F (N) | 10 (m) 6. 10 O 8 m/s 7 m/s O 11.1 m/s O 5.29 m/s

College Physics

1st Edition

ISBN:9781938168000

Author:Paul Peter Urone, Roger Hinrichs

Publisher:Paul Peter Urone, Roger Hinrichs

Chapter7: Work, Energy, And Energy Resources

Section: Chapter Questions

Problem 20PE: A 100-g toy car is propelled by a compressed spring that starts it moving. The car follows the...

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A 100-g toy car is propelled by a compressed spring that starts it moving. The car follows the curved track in Figure 7.39. Show that the final speed of the toy car is 0.687 m/s if its initial speed is 2.00 m/s and it coasts up the frictionless slope, gaining 0.180 m in altitude. Figure 7.39 A toy car moves up a sloped track. (credit: Leszek Leszczynski, Flickr)
Calculate the power output in watts and horsepower of a shot-putter who takes 1.20 s to accelerate the 7.27-kg shot from rest to 14.0 m/s, while raising it 0.800 m. (Do not include the power produced to accelerate his body.) Figure 7.42 Shot putter at the Dornoch Highland Gathering in 2007. (credit: John Haslam, Flickr)
A light spring with spring constant 1.20 103 N/m hangs from an elevated support. From its lower end hangs a second light spring, which has spring constant 1.80 103 N/m. A 1.50-kg object hangs at rest from the lower end of the second spring, (a) Find the total extension distance of the pair of springs, (b) Find the effective spring constant of the pair of springs as a system. We describe these springs as being in series. Hint: Consider the forces on each spring separately.
A sprinter of mass m accelerates uniformly from rest to velocity v in t seconds. (a) Write a symbolic expression for the instantaneous mechanical power P required by the sprinter in terms of force F and velocity v. (b) Use Newtons second law and a kinematic equation for the velocity at any time to obtain an expression for the instantaneous power in terms of m, a, and t only. (c) If a 75.0-kg sprinter reaches a speed of 11.0 m/s in 5.00 s, calculate the sprinters acceleration, assuming it to be constant. (d) Calculate the 75.0-kg sprinters instantaneous mechanical power as a function of time t and (e) give the maximum rate at which he burns Calories during the sprint, assuming 25% efficiency of conversion form food energy to mechanical energy.
A hummingbird hovers by exerting a downward force on the air equal, on average, to its weight. By Newtons third law, the air exerts an upward force of the same magnitude on the birds wings. Find the average mechanical power delivered by a 3.00-g hummingbird while hovering if its wings beat 80.0 times per second through a stroke 3.50 cm long.
A 30.0-kg child starting from rest slides down a water slide with a vertical height of 10.0 m. What is the childs speed (a) halfway down the slides vertical distance and (b) three-fourths of the way down? (Neglect friction.)
A cart is set rolling across a level table, al the same speed on every trial. If it runs into a patch of sand, the cart exerts on the sand an average horizontal force of 6 N and travels a distance of 6 cm through the sand as it comes to a stop. If instead the cart runs into a patch of Hour, it rolls an average of 18 cm before stopping. What is the average magnitude of the horizontal force the cart exerts on the flour? (a) 2 N (b) 3 N (c) 6 N (d) 18 N (e) none of those answers
. A motorist runs out of gas on a level road 200 m from a gas station. The driver pushes the 1.200-kg car to the gas station. If a 150-N force is required to keep the car moving, how much work does the driver do?
Review. You can think of the workkinetic energy theorem as a second theory of motion, parallel to Newtons laws in describing how outside influences affect the motion of an object. In this problem, solve parts (a), (b), and (c) separately from parts (d) and (e) so you can compare the predictions of the two theories. A 15.0-g bullet is accelerated from rest to a speed of 780 m/s in a rifle barrel of length 72.0 cm. (a) Find the kinetic energy of the bullet as it leaves the barrel. (b) Use the workkinetic energy theorem to find the net work that is done on the bullet. (c) Use your result to part (b) to find the magnitude of the average net force that acted on the bullet while it was in the barrel. (d) Now model the bullet as a particle under constant acceleration. Find the constant acceleration of a bullet that starts from rest and gains a speed of 780 m/s over a distance of 72.0 cm. (e) Modeling the bullet as a particle under a net force, find the net force that acted on it during its acceleration. (f) What conclusion can you draw from comparing your results of parts (c) and (e)?
Compare the kinetic energy of a 20,000-kg truck moving at 110 km/h with that of an 80.0-kg astronaut in orbit moving at 27,500 km/h.
Confirm the value given for the kinetic energy of an aircraft carrier in Table 7.1. You will need to look up the definition of a nautical mile (1knot=1nauticalmile/h) .
Two stones, one with twice the mass of the other, are thrown straight up and rise to the same height h. Compare their changes in gravitational potential energy (choose one): (a) They rise to the same height, so the stone with twice the mass has twice the change in gravitational potential energy. (b) They rise to the same height, so they have the same change in gravitational potential energy. (c) The answer depends on their speeds at height h.