Physics 40S Problems Work, Kinetic Energy and Momentum
1. A constant 20.0 N force acts for 10.0 s on a 5.00 kg object, which is initially at rest.
a) What is the object’s final momentum?
b) What is the object’s final kinetic energy?
c) How much work was done in accelerating the body?
d) What distance did the body move?
2. Suppose 12,500 J of work is done on a body that was initially at rest. If its final
velocity was 50 m/s, find the mass of the body.
3. A 10 kg mass is moving with a constant velocity of 10.0 m/s.
a) How much work must be done to double the speed to 20.0 m/s?
b) How much work must be done to halve the original speed to 5.00 m/s?
4. A 2.00kg mass moving at 20.0 m/s has the same momentum as a 10.0kg mass.
a) What is the velocity of the 10.0kg mass?
b) What is the kinetic energy of each of the masses?
5. A 10.0kg body has a kinetic energy ( Ek ) of 500.0 J. What is its momentum?
6. A 10.0kg body at rest on a frictionless table receives an impulse of 30 Ns. What is its
final kinetic energy?
7. A hockey puck of mass 0.200kg is travelling at 20.0 m/s.
a) What is its kinetic energy?
b) How much work was done to give it this velocity?
c) What is its momentum?
8. A force of 20.0 N acts for a distance of 30.0m on a 10kg object, which was originally
at rest. Find its final velocity.
9. The retarding force of –4.00 N acts for a
distance of 15.0m on the object. What is the
final velocity of the object?
10 m/s
4 kg
10. Through what distance
must the 2.00 N force act, in
order to change the velocity of
the 8.00kg mass from 5.00m/s
to 25.0m/s?
8 kg
5 m/s
Fapplied = 2 N
8 kg
25 m/s
11. At a time when the block has moved
12.0 metres, find:
a) Ek at that time (two ways)
b) Work done to overcome
friction
c) Total work done by the applied
force (two ways)
Ff = 4 N
12. A force acts at an angle as shown. When the
object has moved 50.0 metres, find:
a) Ek of the block (two ways)
b) velocity of the block
8 kg
Fapp = 24 N
80 N
66.4
4 kg
13. The 10.0kg object on a frictionless surface is pulled with a force of 60.0 N at an
angle of 53.1 degrees with the horizontal. The object is moved 20.0 metres. What is the
a) Kinetic energy
b) Velocity of the object at that time
14. A force of 120 N acts at an angle on a block as shown. The force of friction is
–8.0 N. The block moves 100m. At that time, find:
a) Ek of block (two ways)
-8N
b) Work done against friction
c) Total work done by the applied force (two ways)
120 N
66.4
20 kg
15. A 160 N force acts at an angle as shown, and the force
of friction is –40.0 N. When the mass has moved 40.0 metres, find:
a) Kinetic energy of the mass
b) Velocity of the mass
c) Work done against friction
-40N
d) Total work done
160 N
41.4
16 kg
Answers
1.
a) 200 kgm/s b) 4000 J c) 4000 J d) 200 m
2.
10 kg
3.
a) 1500 J b) -375 J
4.
a) 4 m/s b) 400 J, 80 J
5.
100 kgm/s
6.
45 J
7.
a) 40J b)40 J c)4 kgm/s
8.
11 m/s
9.
8.37 m/s
10. 1200 m
11. a) 240 J b) 48 J c) 288 J
12. a) 1600 J b) 28.3 m/s
13. a) 721 J b) 12 m/s
14. a) 4000 J b) 800 J c) 4800 J
15. a) 3200 J b) 20 m/s c) 1600 J d) 4800 J