Unit 2 Review Questions
1. A toy gun fires a 9.41-g projectile disc by using a compressed spring (k = 1.72  103 N/m) and a 13.1 cm long
barrel. As the disc travels through the barrel, it experiences a constant frictional force of 0.13 N. If the spring
is compressed 14 mm, what is the speed of the disc as it leaves the gun?
2. A 23-kg block slides 18 m on level ground before coming to rest. If 430 J of work are done by friction,
calculate the coefficient of friction between the block and the ground.
3. A robin of mass 110 g speeds up from 12.3 m/s to 15.4 m/s in level flight. Calculate how much work is done
by the robin.
4. A ball starts from rest and rolls 5.8 m down a short ramp so that it drops 1.8 m vertically. Calculate the
acceleration of the ball.
5. A spring is suspended from a ceiling and a 256-g mass is attached to it and pulled down to stretch the spring
by 18.2 cm. The mass is released and travels through the equilibrium position with a speed of 0.746 m/s.
Calculate the force constant of the spring.
6. A 34-g bullet traveling at 120 m/s embeds itself in a wooden block on a smooth surface. The block then slides
toward a spring and collides with it. The block compresses the spring (k = 99 N/m) a maximum of 1.2 cm.
Calculate the mass of the block of wood.
7. A 0.40-kg cue ball makes a glancing blow to a stationary 0.30-kg billiard ball so that the cue ball deflects with
a speed of 1.2 m/s at an angle of 30.0º from its original path. Calculate the original speed of the cue ball if the
billiard ball ends up traveling at 1.5 m/s.
8. Two carts of mass 12 kg and 15 kg move toward each other with speeds of 2.3 m/s and 1.5 m/s respectively.
If the collision between them is completely inelastic, calculate the velocity of the 15-kg cart after the
collision.
9. Calculate the value of the gravitational field strength g, 250 km above the surface of Earth.
10. How much work is done against gravity to fire a 7.2  102-kg weather monitor 120 km into the air? (rE = 6.38
 106 m, ME = 5.98  1024 kg)
11. Calculate the speed of a satellite in orbit 9.5  103 km above Jupiter. (rJ = 7.18  107 m, MJ = 1.90  1027 kg).
12. The mass of Mars is 6.4  1023 kg. If g = 3.7 N/kg on Mars, what is the radius of Mars?
13. A satellite is in orbit around Earth at an altitude of 3700 km. How much must its speed increase, in kilometers
per hour, to escape Earth’s force of gravity?
14. The average radius of orbit for Jupiter is 7.78  1011 m. Using CS = 3.355  1018 m3/s2, calculate the number
of Earth years it will take for Jupiter to complete one orbit.
Unit 3 Review
Answer Section
PROBLEM
1. ANS:
Using conservation of energy
The speed of the disc is 1.8 m/s.
REF: K/U
2. ANS:
OBJ: 4.5
LOC: EM1.03
The coefficient of friction is 0.11.
REF: K/U
3. ANS:
OBJ: 4.1
LOC: EM1.01
The robin must do 4.7 J of work to increase its speed.
REF: K/U
OBJ: 4.2
LOC: EM1.01
4. ANS:
First use conservation of energy. Since the ball is not moving at the top, it has no Eg, and we will choose our
reference point so at the bottom it has no EK.
Only the positive square root applies (speed).
Use this as vf in the kinematics equation:
The acceleration of the ball is 3.0 m/s2.
REF: K/U
OBJ: 4.4
5. ANS:
Using conservation of energy,
LOC: EM1.03
The spring constant is 31.9 N/m
REF: K/U
OBJ: 4.5
LOC: EM1.03
6. ANS:
Momentum is conserved during the collision.
Conserved energy for the spring compression:
Now sub in to calculate the mass of the wooden block
The mass of the wooden block is 12 kg.
REF: K/U
OBJ: 5.3
LOC: EM1.02
7. ANS:
We will choose the original direction of motion of the cue ball as the +x direction.
Using vector components in the y-direction,
Using vector components in the x-direction:
The initial speed of the cue ball was 2.0 m/s.
REF: K/U
OBJ: 5.4
LOC: EM1.03
8. ANS:
Choose the original direction of the 12-kg cart as the +x direction.
The final speed of the 15-kg cart is 0.19 m/s.
REF: K/U
9. ANS:
OBJ: 5.3
LOC: EM1.02
The gravitational field strength 250 km above Earth is 9.1 N/kg.
REF: K/U
10. ANS:
OBJ: 6.1
LOC: EM1.06
The work
done against gravity is 8.3  108 J.
REF: K/U
OBJ: 6.3
LOC: EM1.07
11. ANS:
The radius of orbit is rO = 7.18  107 m + 9.5  106 m = 8.13  107 m
The speed of the satellite is 3.9  104 m/s.
REF: K/U
12. ANS:
OBJ: 6.2
LOC: EM1.07
The radius of Mars is 3.4  106 m.
REF: K/U
OBJ: 6.1
13. ANS:
First calculate the speed satellite in orbit:
LOC: EM1.06
Additional energy required to bring the object to a total energy of zero:
8896 – 6292 = 2604 m/s, or 9.4  103 km/h.
The satellite must speed up 9.4  103 km/h to leave Earth’s gravity.
REF: K/U
OBJ: 6.3
14. ANS:
First calculate the period in seconds:
LOC: EM1.07
Now convert to Earth years:
Jupiter takes 11.9 Earth years to make one orbit.
REF:
K/U
OBJ: 6.2
LOC: EM1.06