Page 228 - Physics

Physics for Secondary Schools
the kinetic energy at 45 m/s than at
15 m/s?
11. Rock A has a mass of 2 kg and a
speed of 1 m/s. Rock B has a mass
of 1 kg and a speed of 2 m/s. Which
rock has more kinetic energy?
12. If your mass is 45 kg, how much
work would you do in climbing a
ladder that is 5 m high?
13. The total mass of a wheelbarrow and
its load is 90 kg. A worker pushes
the wheelbarrow and loads up a plank
of length 2.0 m onto a platform. The
platform is at a height of 0.65 m above
the ground as shown in Figure 9.29.
300 N
Platform
2 m
0.65 m
Figure 9.29
If the worker exerts a force of 300 N
on the wheelbarrow in the direction
in which the wheelbarrow moves.
(i) Calculate the gravitational
potential energy gained by the
wheelbarrow and its load.
(ii) Calculate the work done on the
wheelbarrow by the worker,
after moving by 2 m.
(iii) Suggest a reason as to why
the answers in (i) and (ii) are
different.
14. (a) Discuss the energy changes in
a fi rework.
222
Physics Form 1 Final.indd 222
(b) A 3.00 kg object is lifted from
the fl oor and placed on a shelf
that is 2.50 m above the fl oor.
(i) What was the work done in
lifting the object?
(ii) What is the gravitational
potential energy of the object
sitting on the shelf?
(iii) If the object falls off the shelf
and falls to the fl oor, what will
its velocity be when it hits the
fl oor? ignore air resistance.
15. Which object has more kinetic energy
between a 10 kg object travelling at
5 m/s and a 5 kg object travelling at
10 m/s?
16. How much work is required to stop
a 1 500 kg car travelling at 20 m/s?
17. A 2 kg object is on a tabletop 1.1
m above the fl oor. How much work
is required to lift it at a constant
velocity to a shelf 1.3 m above the
fl oor?
18. A 0.5 kg ball is dropped from a
height of 2.3 m above the fl oor. If
upon hitting the fl oor it loses 3 J of
energy, how high will it bounce?
19. A 3 kg box starts sliding down a
hill that is 3.3 m high with an initial
velocity of 5 m/s. If on reaching the
bottom of the hill its velocity is
7.5 m/s, how much work is done by
the box to overcome friction?
20. A student pulls a spring with a spring
constant k=120 N/m stretching it
from its rest length of 0.10 m to 0.20
m. Determine the elastic potential
energy stored in the spring.
Student’s Book Form One
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