Page 4 - TRIAL 2

Example 2 d = 333.333m
c) Explain

No. The car crashes the tree because the distance
of the car to stop is 333m exceed than the actual
distance 100m.

d) W = Fd
= 1333.32(100)
= 133332 J

The car with mass 1800 kg is moving from rest to K.E= W
1
2
80km/hour in 10 minutes heading towards urban, 133332 =
2
suddenly lost control at the middle of the journey
1 2
a) Find the force that react on the car. = (1800)
2
b) Calculate the distance of the car in which to v = 12.172 m/s
stop after he fully applies his brakes
c) Explain, can the driver avoid crashing the e) FR=?
tree? Fa = Fx = 1333.32N
d) Calculate the velocity that can save the Fy= w = mg
incident happened = 1800(9.81)
e) Find the resultant force of the car between =17658 N
the action force and the gravity force.
2
2
2
f) Calculate the power that generate from the = +
car before crash. = 17658 + 133332
2
2
FR = 134496.20N

Solution
a) u = 80km/hr x 1000m / 1km x 1hr/3600s f) Power=?
= 22.222 m/s
P = Fv
v=0 (car stop); = 1333.32(22.222)
= 29629.037 Watt
1
t = min x 60s/1 min= 30 s
2

− 4.2 Energy
a =

0− 22.222
=
30
= -0.741m/s 1. All living things on earth need energy to do
work.
F= ma 2. Energy is defined as the ability to do work.
= 1800(0.741)
= 1333.32 N 3. Energy is a scalar quantity and its unit is Joule
(J).
b) Distance of the car, d=? 4. Energy exists in many forms. For example,
potential energy, kinetic energy, heat energy,
1
2
W = K.E= electrical energy, sound energy and wind
2
1 2 energy.
= (1800)22.222
2
= 444435.556 J 5. Work is done when energy is converted from
one form to another form.
W =Fd
444435.556 = 1333.32d
Kinetic Energy
3