Advertisements
Advertisements
Question
For the following scenario, state whether the work done by gravity is positive, negative, or zero.
A person climbs a ladder.
Advertisements
Solution
Negative work is done.
Explanation:
When a person climbs a ladder (upward), the displacement covered by the person is opposite to the direction of the force of gravity (downward), so the work done on the person by the force of gravity is negative.
RELATED QUESTIONS
If the power of a motor is 100 kW, at what speed can it raise a load of 50,000 N?
When a body moves in a circular path, how much work is done by the body? Give reason.
(Hint: The body is acted upon by the centripetal force.)
A boy weighing 350 N climbs up 30 steps, each 20 cm high in 1 minute, Calculate:
- the work done and
- power spent.
State the condition when a force produces
(i) linear motion.
(ii) rotational motion, in a body.
What do you mean by uniform circular motion?
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"]`
Justify the statement. “Power can be expressed as the product of force and velocity.”
The world record for weight lifting was held by Sergei Didyk of the USSR. He lifted 261 kg to a height of 2.3 m in 4s; find:
(a) Weight lifted by him
(b) Work done by him
(c) Power developed by him. (g = 10m/s2)
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.
