EXERCISES. DYNAMICS. DBH 3 ESO.
1. The mass of a car is 1200kg and its acceleration 0.8m/s2

. Calculate the force applied by

the car ́s motor.
2. Calculate:
A) the force needed by a 5kg car to move with uniform velocity.
B) the force a 0.5kg car needs to move with an acceleration of 20m/s2
C) the mass of a car that reaches an acceleration of 2m/s2 when we apply a force of 20N
3. A 5kg body is at rest when we apply a force of 10N, so the car obtains a velocity of
20m/s. Calculate both the acceleration and the time needed to obtain that acceleration.
4. A body at rest receives during 5s a force of 500N, so its velocity raises to 20m/s.
Calculate the mass of the body.
5. A 1000kg body moves with a 72km/h velocity and it ́s able to stop completely after 24s.
Calculate the force of the brakes.
6. A car that moves at 72km/h velocity is able to stop completely in 8s. Calculate the force
of the brakes if we know that the mass of the car is 800kg.
7. A 3kg body receives during 3s an unknown force that changes its velocity from 1m/s to
5m/s. Calculate the intensity of that force.
8. Calculate the time needed to apply a 50N force to a 10kg car that is at rest to change its
velocity to 20m/s.
9. A 1200kg car is moving at 80km/h velocity when we apply the brakes and in 10s it stops
completely. Calculate the force of the brakes.
10. A 100kg motorcycle moves at a 65km/h velocity. This bike is able to halve this velocity
in 15s. Calculate the force needed.
11. An engine applies a force of 20N. Knowing that the force of friction is 8N, calculate the
net force, the acceleration (consider 3kg of mass) and the coefficient of friction.
12. A 400kg object is at rest and 5s later, its velocity is 600m/s. Calculate the acceleration
and the force we must apply. This object enters a new road where the coefficient of friction
is 0,4. Calculate the force we need to apply so the acceleration doesn ́t change.
13. A 50kg brick is at rest and we apply a force parallel to the ground of 200N during 3s. If
the coefficient of friction is 0,25, calculate the final velocity.
14. We apply a 1000N force of friction to a car moving at a 72km/h velocity. Calculate the
force we must apply so the velocity remains constant.
15. Upon a 5kg object we apply a force of 50N. The coefficient of friction is 0,1 in this road.
Calculate the velocity it will have 5s later and the acceleration of the movement.

16. Paula and Miren want to move a 40kg block and for that purpose, they pull with 300N
and 10N respectively. Raul pulls in the opposite sense with a force of 30N. Calculate: the
net force and the acceleration of the block.
17. We apply a force of 100N during 3s to a body that is at rest so its velocity changes to
30m/s. Calculate the mass of the body. Suppose that the road coefficient of friction is 0,3;
calculate now the force we must apply so the acceleration doesn ́t change.
18. The engine of a car produces a force of 4500N. If the force of friction is 1300N and the
mass of the car is 860kg, calculate the velocity it will have after 10s of movement (at first it
was at rest)
19. A 10kg body is at rest and we apply a 30N force parallel to the ground so it moves.
Calculate the acceleration and the velocity it will have after 5s.
20. We apply a 600N force to a body on the floor so it takes a velocity of 30m/s in 5s.
Calculate the mass of the object.
21. The engine of a 500kg car produces a force of 2000N. If the coefficient of friction
between the road and the car is 0,2, calculate the net force, the acceleration of the car and
the velocity the car will have after 10s.
22. A 10kg body receives a force of 30N. If the force of friction is 12N, calculate after 8s
the body ́s velocity.
23. A car that is moving at a 72km/h velocity enters a stony road, so it stops after a while.
If the coefficient of friction is 0,4, calculate the time needed to stop. (Hint: there ́s no
force applied)
24. A 10kg body is at rest. We apply a force and due to that, 10s later the velocity is
30m/s. If the force of friction is 50N, calculate the force applied.
25. A 50kg body receives a 150N force. Calculate the acceleration it will gain without force
of friction and with a force of friction of 60N.