Download work and energy - Indian School Al Wadi Al Kabir

INDIAN SCHOOL AL WADI AL KABIR
DEPARTMENT OF SCIENCE
CLASS IX
W.S. No.4
Physics
Topic: Work and Energy
DATE:
Name:
Answer the following in one word or one sentence. Each question carries 1
mark
1) Define commercial unit of energy.
2) How much work is done by a weight lifter when he holds a weight of 80 kg on his shoulders
for two minutes?
3) In the figure given below, if the bob of the pendulum swings from B to C,
What is the kinetic energy at C?
4) A child winds his toy car by moving its key. Name the type of energy stored in the car.
5) Convert one commercial unit of energy into Joules.
Answer the following in about 30 words. Each question carries 2 marks.
6) A car with a speed of 25 m/s weighing 900 kg stops at a distance of 40 m. Calculate the force
exerted and the work done by the brakes?
Answer the following question in 50 words each. Each question carries
3marks each.
7) a) The potential energy of a freely falling body decreases progressively. What happens to its
(i) Kinetic energy (ii) Total energy? State the law on which your answer is based.
8) A boy of mass 45 kg climbs up 20 steps in 20 s.If each step is 25 cm high, calculate the
power of the boy used in climbing. (Take g= 10m/s2) [2011 SA 2 ISWK].
9) Seema tried to push a heavy rock of mass 100 kg for 200 s, but could not move it. Find the
work done by Seema at the end of 200s.Find out the power delivered by her. Give reason to
justify the answer.
10) Distinguish between positive work and negative work. When you lift an object up, two forces
act on it. Identify these forces. Which one of the two does
(a) Positive work
(b) Negative work?
Justify your answer.
11) Define power. Derive its SI unit. An electric bulb is rated 10 W. What does it mean? What is
the energy consumed in joules if it is used for 5 minutes?
Answer the following questions in about 70 words. The questions carry
5 marks
12) A body of mass m is moving in a circle of radius ‘r’ with a constant speed ‘v’.The force on
the body is mv2/r and is directed towards the Centre. Calculate the work done in moving the
body
(a) Half the circumference of the circle
(b) ¼ of the circumference of the circle
(c) Complete circumference
(d) ¾ of the circumference of the circle
[2013 SA 2 ISWK]
13) Define the term potential energy. State its SI unit.
Derive an expression for potential energy of an object of mass ‘m’ that is raised to a height
‘h’ above the ground.
An object of mass 40 kg is raised to a height of 5m above the ground. What is its potential
energy? If the object is allowed to fall find the kinetic energy half way down. [g=10 m/s2]
[2011 SA 2 ISWK]
14) (a) Define kinetic energy. Derive a relation for the same.
(b) If 500 J of K.E is associated with a 5 kg mass, find the velocity of the body.
Prepared by Ms. Jenesha J