Advertisements
Advertisements
Question
Each of the following statement describes a force acting. Which force is causing work to be done?
Options
the weight of a book at rest on a table
the pull of a moving railway engine on its coaches
the tension in an elastic band wrapped around a parcel
the push of a person's feet when standing on the floor
Advertisements
Solution
We will justify all statements one by one as:
(a) The weight of a book at rest on a table cannot do any work as the book is at rest. So, the work done by this force is zero.
(b) The pulling force applied by the railway engine on its coaches is doing work, as the force applied by the engine results in the motion of the coaches.
(c) The tension force in an elastic band wrapped around a parcel cannot do any work, as there is no motion of the parcel because of the tension force of the rubber band.
(d) The push of a person’s feet on a floor when he is standing cannot do any work because there is no motion involved due to the applied force.
Therefore, the answer is -
(b) The pull of a moving railway engine on its coaches.
APPEARS IN
RELATED QUESTIONS
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
It takes 20 s for a person A of mass 50 kg to climb up the stairs, while another person B does the same in 15 s. Compare the work done.
A water pump raises 50 litres of water through a height of 25 m in 5 s. Calculate the power of the pump required.
(Take g = 10 N kg-1 and density of water = 1000 kg m-3)
When you move upstairs, do you perform some work?
A boy of mass m climbs up a staircase of vertical height h.
- What is the work done by the boy against the force of gravity?
- What would have been the work done if he uses a lift in climbing the same vertical height?
Name the physical quantity associated with the 'rate of doing work'.
In what way does an ‘Ideal machine’ differ from a ‘Practical machine’?
(i) A 200g ball is thrown vertically upward with an initial velocity of 30 ms-1. Draw a velocity-time graph for the motion of ball.
(ii) How long will the ball take to reach the highest point?
(iii) What will be the kinetic energy of ball, when it returns to the starting point, neglecting the air resistance?
(iv) What will be the potential energy of ball at highest point?
A truck driver can load oil drums into the back of the truck by pushing them up a sloping plank, or by lifting them directly. Each drum has a mass of 80 kg, the plank is 3 m long, and the back of the truck is 0.8 m above the ground.
(i) How much force would be needed to lift a drum into the truck directly/without using the plank? (Take g = 10 m/s2)
(ii) How much energy would be required in lifting the drum into the truck without the plank?
(iii) If the force needed to push the drum up the plank is 300 N, why is this less than the answer to part (i)?
(iv) When the truck is loaded, the driver drives off. List the major energy changes that take place in moving the truck.
(v) The driver has to stop at the factory gates. What happens to the kinetic energy of the truck?
