LO4 REVISION
1. A mechanic pushes a 2.50 X 103-kg car from rest to a speed of v, doing 5 000 J of work in the
process. During this time, the car moves 25.0 m. Neglecting friction between car and road, find
the horizontal force exerted on the car. (Ans 200N)
2. A 7.00-kg bowling ball moves at 3.00 m/s. How fast must a 2.45-g Ping-Pong ball move so that
the two balls have the same kinetic energy? ( 160 m/s)
3. A child and a sled with a combined mass of 50.0 kg slide down a frictionless slope. If the sled
starts from rest and has a speed of 3.00 m/s at the bottom, what is the height of the hill? (0.459
m)
4.
The work done by a force which is perpendicular to the displacement is _________.
a.
b.
c.
d.
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negative
greater than zero
zero
none of the above
5.
Which form of energy does flowing water possess?
a.
b.
c.
d.
gravitational energy
potential energy
electrical energy
kinetic energy
6.
A bullet whose initial kinetic energy is 400 J strikes a block where an 8000-N resistive force
brings it to a stop. The depth of penetration into the wood is approximately ____.
a.
unknown for lack of information
b.
0.2 m
c.
0.5 m
d.
0.05 m
7.
An object falling from airplane has a velocity of 55 m/s. If its potential energy at that point
is one-half of its kinetic energy, what is its height above the earth?
8.
A 78-kg skydiver has a speed of 62 m/s at an altitude of 870 m above the ground.
a. Determine the kinetic energy possessed by the skydiver.
b. Determine the potential energy possessed by the skydiver.
c. Determine the total mechanical energy possessed by the skydiver.
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9.
A bicycle has a kinetic energy of 124 J. What kinetic energy would the bicycle have if it had
…
a. … twice the mass and was moving at the same speed?
b. … the same mass and was moving with twice the speed?
c. … one-half the mass and was moving with twice the speed?
d. … the same mass and was moving with one-half the speed?
e. … three times the mass and was moving with one-half the speed?
10. A block is pulled 7.00 m across a frictionless surface by means of a rope. The rope tension is
40.0 N; and the net work done on the block is 247 J. What angle does the rope make with the
horizontal? Ans ( 28.1°)
11. The kinetic energy of a car is 8.00×106 J as it travels along a horizontal road. How much work
is required to stop the car in 10 s?( 8.00 ×106 J)
12.
A skier leaves the top of a slope with an initial speed of 5.00 m/s. Her speed at the bottom of
the slope is 13.0 m/s. What is the height of the slope? (7.34m)
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13. A 1.2 kg brick is held a distance of 2 m above a manhole and then dropped. The bottom of the
manhole is 3 m below the street. Relative to the street, what is the potential energy at each
location? What is the change in potential energy?
14. A 4-kg hammer is lifted to a height of 10 m and dropped. What are the potential and kinetic
energies of the hammer when it has fallen to a point 4 m from the Earth? What is the total energy
when
15. A runaway, 400-kg wagon enters a cornfield with a velocity of 12 m/s and eventually comes to
rest. What work was done on the wagon?
LO5 REVISION
1. A 0.2-kg baseball traveling to the left at 20 m/s is driven in the opposite direction at 35 m/s when
it is hit by a bat. The average force on the ball is 6400 N. How long was it in contact with the bat?
Ans. 1.72 ms
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2. A car traveling at 8 m/s crashes into a car of identical mass stopped at a traffic light. What is the
velocity of the wreckage immediately after the crash, assuming that the cars stick together?
3.
The coefficient of restitution for steel is 0.90. If a steel ball is dropped from a height of 7 m, how
high will it rebound?
Ans. 5.67 m
4.
A 300-g block moving north at 50 cm/s collides with a 200-g block moving south at 100 cm/s.
If the collision is completely inelastic, what is the common velocity of the blocks after they
stick together? What is the loss in energy?
5.
A 2500-kg truck traveling at 40 km/h strikes a brick wall and comes to a stop in 0.2 s. Ans. (a)
−2.78 × 104 kg · m/s, (b) −2.78 × 104 N · s, (c) 1.39 × 105 N
(a) What is the change in momentum?
(b) What is the impulse?
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(c) What is the average force on the wall during the crash?
6. The face of a golf club exerts an average force of 4000 N while it is in contact with the golf
ball. If the impulse is 80 N s, the time of contact is ____.
a.
0.2 s
b.
0.02s
c.
2s
d.
0.002 s
7.
A ball dropped from a height of 8.0 m from the floor. If the ball rebounds to a height of 2.0
m, the coefficient of restitution is _________.
e.
4.0
f.
2.0
g.
0.25
h.
0.50
8. The value of ‘e’ for a perfectly elastic collision is ___
a.
0
b.
-1
c.
1
d.
none of the above
9. A ball of mass 1.2 kg moving with a velocity of 30 m/s comes to rest after hitting the wall.
Calculate the momentum of the ball before it hit the wall.
a.
36 kg.m/s
b.
6 kg.m/s
c.
360 kg.m/s
d.
Cannot be calculated.
10. A 1-kg mass slides with a velocity of 15 m/s toward a 2-kg mass initially at rest as shown in
figure below. All surfaces are frictionless. What is their common velocity if they stick together
on colliding?
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11. A 0.2-kg baseball traveling to the left at 23 m/s is driven in the opposite direction at 38 m/s
when it is hit by a bat. The average force on the ball is 6500 N. How long was it in contact
with the bat?
12. A 20-kg child is at rest in a wagon. The child jumps forward at 2 m/s, sending the wagon
backward at 12 m/s. What is the mass of the wagon? Ans. 3.33 kg
13. A 50.0-kg boy runs at a speed of 10.0 m/s and jumps onto a cart as shown in the figure. The
cart is initially at rest. If the speed of the cart with the boy on it is 2.50 m/s, what is the mass of
the cart?
(a)
150 kg (c) 210 kg (e) 300 kg (b) 175 kg (d) 260 kg
14. A 20-kg girl and a boy on roller skates stand at rest facing each other. They push each other as
hard as they can, and the boy moves to the left with a velocity of 2 m/s, while the girl moves
to the right with a velocity of 3 m/s. What is the mass of the boy?
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LO3 –REVISION
1. Determine the resultant torque about the corner A for Fig.
2. A 60-N cube and a 20-N cube are connected by a light rod 600 mm in length. How far from
the middle of the 60-N cube is the center of gravity?
a.
b.
c.
d.
105 mm
150 mm
89.5 mm
200 mm
600mm
60 N
20 N
3. Find the single upward force required to keep the beam in equilibrium. Where should the
single upward force be located?
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4. Weights of 3, 6, 8 and 10N are hung from a 10m rod at distances of 2, 4, 6, and 8m from
the left end. Neglecting the weight of the rod, how far from the left end is the center of
gravity?
2
4
6
8
6N
8N
10N
10
0
3N
5. Assume that the bar in Fig. 5-16 is of negligible weight. Find the forces F and A provided
the system is in equilibrium.
F
30 cm
80 N
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Axis
90 cm
A
6. Two 8-kg masses are attached to the end of a thin rod 400 mm long. The rod is supported
in the middle and whirled in a circle. The rod can support a maximum tension of
only
800 N. What is the maximum frequency of revolution? [R = (400 mm/2) = 200 mm ]
(v = 4.47 m/s; f = 3.56 rev/s)
7. On a rainy day the coefficient of static friction between tires and the roadway is only 0.4.
What is the maximum speed at which a car can negotiate a turn of radius 80 m? ( vc = 17.7
m/s)
8. A bus negotiates a turn of radius 120 m while traveling at a speed of 96 km/h. If slipping
just begins at this speed, what is the coefficient of static friction between the tires and the
road? [96 km/h = (96 km/h)(1000 m/ 1 km)(1 h/3600 s) = 26.7 m/s]( s = 0.605)
9. A conical pendulum swings in a horizontal circle of radius 30 cm. What angle does the
supporting cord make with the vertical when the liner speed of the mass is 12 m/s?
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10. What is the linear speed of the flyweights in Fig. 10-16 if L = 20 cm and  = 600? What is
L
the frequency of revolution?

R
11. If the length of the L in Fig. 10-16 is 60 cm. What velocity is required to cause the
flyweights to move to an angle of 300 with the vertical? (v = 1.30 m/s)
L

R
Motion in a Vertical Circle
12. A rock rests on the bottom of a bucket moving in a vertical circle of radius 70 cm. What is
the least speed the bucket must have as it rounds the top of the circle if it is to remain in the
bucket?
T
mg
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R
13. A 1.2-kg rock is tied to the end of a 90-cm length of string. The rock is then whirled in a
vertical circle at a constant speed. What is the critical velocity at the top of the path if the
v
string is not to become slack? (vc = 2.97 m/s)
T
mg
R
14. Assume that the rock of Problem 10-32 moves in a vertical circle at a constant speed of 8
m/s? What are the tensions in the rope at the top and bottom of the circle.
(At Top T = 73.6 N; At Bottom T = 97.1 N)
v
T
mg
R
T
v
mg
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