英语翻译

英语翻译
1.Can the speed of an object change if the net work done on it is zero?
2.Discuss whether any work is being done by each of the following agents and,if so,whether the work is positive or negative.
a.a chicken scratching the ground
b.a person reading a sign
c.a crane lifting a bucket of concrete
d.the force of gravity on the bucket in (c)
3.Furniture movers wish to load a truck using a ramp from the ground to the rear of the truck.One of the movers claims that less work would be required if the ramp’s length were increased,reducing its angle with the horizontal.Is this claim valid?Explain.
4.A pendulum swings back and forth,as shown at right.Does the tension force in the string do work on the pendulum bob?Does the force of gravity do work on the bob?Explainyour answers.
5.The drivers of two identical cars heading toward each other apply the brakes at the same instant.The skid marks of one of the cars are twice as long as the skid marks of the other vehicle.Assuming that the brakes of both cars apply the same force,what conclusions can you draw about the motion of the cars?
6.When a punter kicks a football,is he doing work on the ball while his toe is in contact with it?Is he
doing work on the ball after the ball loses contact with his toe?Are any forces doing work on the ball
while the ball is in flight
7.A person lifts a 4.5 kg cement block a vertical distance of 1.2 m and then carries the block horizontally a distance of 7.3 m.Determine the work done by the person and by the force of gravity in this process.
8.A plane designed for vertical takeoff has a mass of 8.0 × 103 kg.Find the net work done by all forces on the plane as it accelerates upward at 1.0 m/s2 through a distance of 30.0 m after starting from rest.