Mechanics | Relativity Answers

A team of dogs drags a 121 kg sled 1.72 km
over a horizontal surface at a constant speed.
The coefficient of friction between the sled
and the snow is 0.205.
The acceleration of gravity is 9.8 m/s
2
.
Find the work done by the dogs.
Answer in units of kJ

Find an expression for the energy density in terms of stress and strain

the speed of a vehicle of mass 500kg increases its velocity from 56km/hr to 72km/hr.what is the increase in kinetic energy.

The drawing shows two boxes resting on frictionless ramps. One box is relatively light and sits on a steep ramp. The other box is heavier and rests on a ramp that is less steep. The boxes are released from rest at A and allowed to slide down the ramps. The two boxes have masses of 9 and 48 kg. If A and B are 5.5 and 0.5 m, respectively, above the ground, determine the speed of (a) the lighter box and (b) the heavier box when each reaches B. (c) What is the ratio of the kinetic energy of the heavier box to that of the lighter box at B?

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A 36-kg girl is bouncing on a trampoline. During a certain interval after leaving the surface of the trampoline, her kinetic energy decreases to 230 J from 460 J. How high does she rise during this interval? Neglect air resistance.

A truck is traveling at 14.9 m/s down a hill when the brakes on all four wheels lock. The hill makes an angle of 11 ° with respect to the horizontal. The coefficient of kinetic friction between the tires and the road is 0.838. How far does the truck skid before coming to a stop?

Suppose the skateboarder shown in the drawing reaches a height of 2.20 m above the right side of the semicircular ramp. He then makes an incomplete midair turn and ends up sliding down the right side of the ramp on his back. When the skateboarder reaches the bottom of the ramp, his speed is 6.00 m/s. The skateboarder's mass is 68.0 kg, and the radius of the semicircular ramp is 3.40 m. What is the average frictional force exerted on the skateboarder by the ramp?


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A 282-kg crate is being pushed across a horizontal floor by a force P that makes an angle of 48.1 ° below the horizontal. The coefficient of kinetic friction is 0.288. What should be the magnitude of P, so that the net work done by it and the kinetic frictional force is zero?

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Complete the following statement: A force that acts on an object is said to be conservative if




it results in a change in the object's kinetic energy.



it obeys Newton's laws of motion.



it always acts in the direction of motion of the object.



the work it does on the object is independent of the path of the motion.



the work it does on the object is equal to the increase in the object's kinetic energy.

The kinetic energy of an 1800-kg truck is 7.2 × 105 J. What is the speed of the truck?