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DKT113 Engineering Physics
Semester 1 Session 2011/12
TUTORIAL 4
1. Define these terms:
i)
work
ii)
kinetic energy
iii)
potential energy
iv)
conservation of energy
v)
work energy theorem
vi)
power
2. Define what is work done on an object of mass m kg by a force f Newton.
3. A sack of mass 5kg was pushed 10m horizontally away from its origin by a force 7
Newton. Calculate how much work had been done on the sack?
4. A force 50N, acts continuously on a crate to displace it by 3.0m. Calculate how much
work had been done on the crate?
5. A space vehicle weighting 40 kg travels in frictionless space at a speed of 100 ms-1.
Immediately after encountering a meteor storm its speed reduces to 88ms -1. (The space
vehicle covers a distance of 200m in the storm) Calculate
i) its initial kinetic energy
ii) its kinetic energy immediately after coming out of meteor storm
iii) the resisting force(average) in the meteor storm
6. A 0.2 kg metal ball is being drop from a 10 m building. How much potential and
kinetic energy does the ball has :
i) at the point of release
ii) just before it hits the ground
iii) half-way before it hits the ground
7. A horizontal spring with k = 0.15N/m was stretched horizontally for 4.0 cm from its origin.
Calculate how much work was done on the spring?
8. A metal ball of mass 10g was attached to the lower side of a vertical spring. Calculate
the spring constant, k if attaching the metal ball makes the spring stretch downwards
by 1.2cm. An external force pulls the metal ball further down by 2.0cm and releases it.
How much energy does this external force supply? What will be the speed of the ball
when it reaches its origin?(Assume that there is no friction, the spring is weightless and
there is no change in gravitational force)
9. A machine lifts a 50kg load 3 m from ground. In doing so, it uses up 2000Joule of
energy. Calculate this machine mechanical efficiency.
10.
i) Explain why at θ=90° work is 0 and
ii) Explain why at θ=180 work is negative
11. Azim pulls 75 kg boxes with rope at the angle, θ 35°. The coefficient of kinetic
friction between the boxes and the floor is 0.7650. If he moves the boxes with a
constant velocity a distance of 9.00 m, how much work is done?
DKT113 Engineering Physics
Semester 1 Session 2011/12
12. The maximum power of a car of mass 1200 kg, when it traveling at a constant
velocity of 30 ms-1 is 90 kW. Calculate the forward thrust of the car engine when
he car is traveling at 30 ms-1.
13. A pulley system is used to raise a load of 2000N through a height of 5 m. The force
of 500 N used to do this moves a distance of 30 m.
a. What is the work done by force?
b. What is the work done by pulley system?
c. What is the efficiency of the system?