Advertisements
Advertisements
Question
For the following scenario, state whether the work done by gravity is positive, negative, or zero.
A car in neutral gear is coming down the slope.
Advertisements
Solution
Positive work is done.
Explanation:
When a car in neutral gear is coming down the slope, the direction of displacement covered by it is parallel to the direction of force of gravity (downwards), so the work done on the car by the force of gravity is positive.
RELATED QUESTIONS
Give the expression for mechanical advantage of an inclined plane in terms of the length of an inclined plane.
State and define the S.I. unit of work.
State two factors on which power spent by a source depends. Explain your answer with examples.
What do you understand by the clockwise and anti clockwise moment of force?
What do you mean by a centrifugal force?
A pump is used to lift 600 kg of water from a depth of 75 m in 10s. Calculate:
- The work done by the pump,
- the power at which the pump works, and
- The power rating of the pump if its efficiency is 40%. (Take g = 10m s-2).
`["Hint" : "Efficiency" = "useful power"/"power input"]`
A boy takes 3 minutes to lift a 20 litre water bucket from a 20 m deep well, while his father does it in 2 minutes.
How much work each does? Take density of water = 103 kg m-3 and g = 9.8 N kg-1.
A force F when acts on a body, displace it by a distance d in a direction at an angle θ with the direction of the force. Write down the expression for the work done by the force.
Calculate the work done when:
A car is moved on a rough road through 30 m against a frictional resistance of 75 N.
A man weighing 700 N runs up a flight of 15 steps, each 20 cm high, in 5 seconds. Calculate the power of the man.
