INTERNATIONAL HOPE SCHOOL BANGLADESH
“Physics_Dynamics”
CLASS TEST “02”
(Class-11)
2023-2024
TIME: 45 mins
NAME:
IHSB NO:
1. A ball of mass 2.0 kg travels horizontally with a speed of 4.0ms-1. The
ball collides with a wall and rebounds in the opposite direction with
a speed of 2.8ms-1. The time of the collision is 150 ms.
What is the average force exerted on the wall?
A 16N
B 37N
C 53N
D 91N
2. An ice-hockey puck of mass 150g moves with an initial speed of 2.0ms along the
surface of an ice rink.
The puck slides a distance of 30m in a straight line before stopping.
What is the average frictional force acting on the puck?
A 0.010N
B 0.020N
C 0.067 N
D 0.44N
3. A resultant force 30N acts on an initially stationary mass of 10 kg for 4.0s. How far
does the mass move?
A 6.0m
B 12m
C 24m
D 48m
4. A pendulum bob is held stationary by a horizontal force H. The three forces acting on
the bob are shown in the diagram.
5. The tension in the string of the pendulum is T. The weight of the pendulum bob is W.
The string is held at an angle of 30° to the vertical.
Which statement is correct?
6. A stationary firework explodes into three pieces. The masses and the velocities of the
three pieces immediately after the explosion are shown.
What are speed v₁ and speed v₂?
7. A book rests on a horizontal table. A metal block rests on the top of the book as
shown in Fig. 3.25. Newton's third law describes how forces exist in pairs.
One such pair of forces is the weight of the book and another force Y. What is the name of
the body on which force Y acts?
A book
B Earth
C ground
D metal block
8. A book of weight W is at rest on a table. A student attempts to state Newton's third
law of motion by saying that 'action equals reaction'.
If the weight of the book is the 'action' force, what is the 'reaction' force?
A the force W acting downwards on the Earth from the table
B the force W acting upwards on the book from the table
C the force W acting upwards on the Earth from the book
D the force W acting upwards on the table from the floor
9. A golf ball of mass m is dropped onto a hard surface from a height h1, and rebounds to
a height h2.
The momentum of the golf ball just as it reaches the surface is different from its momentum
just as it leaves the surface.
What is the total change in the momentum of the golf ball between these two instants?
(Ignore air resistance.)
10. Two spheres approach each other along the same straight line. Their speeds are
u1 and u2 before collision. After collision, the spheres separate with speeds v 1 and v2 in
the directions shown below.
Which equation must be correct if the collision is perfectly elastic?
1. A small remote-controlled model aircraft has two propellers, each of diameter 16 cm.
Fig. 3.1 is a side view of the aircraft when hovering.
Air is propelled vertically downwards by each propeller so that the aircraft hovers at a fixed
position. The density of the air is 1.2 kg m-3. Assume that the air from each propeller moves
with a constant speed of 7.6 m s-1 in a uniform cylinder of diameter 16 cm. Also assume that
the air above each propeller is stationary.
(a) Show that, in a time interval of 3.0 s, the mass of air propelled downwards by one
propeller is 0.55 kg.
[3]
(b) Calculate:
(i) the increase in momentum of the mass of air in (a)
[2]
(ii) the downward force exerted on this mass of air by the propeller.
[1]
(c) State:
(i) the upward force acting on one propeller
[1]
(ii) the name of the law that explains the relationship between the force in (b)(ii) and the
force in (c)(i).
[1]
(d) Determine the mass of the aircraft.
[1]
(e) In order for the aircraft to hover at a very high altitude (height), the propellers must
propel the air downwards with a greater speed than when the aircraft hovers at a low
altitude. Suggest the reason for this.
[1]
2 (a) Fig. 2.1 shows the velocity-time graph for an object moving in a straight line.
(i) Determine an expression, in terms of u, v and t, for the area under the graph.
[1]
(ii) State the name of the quantity represented by the area under the graph.
[1]
(b) A ball is kicked with a velocity of 15ms-1 at an angle of 60° to horizontal ground. The ball
then strikes a vertical wall at the instant when the path of the ball becomes horizontal, as
shown in Fig. 2.2.
(b) A ball is kicked with a velocity of 15ms-1 at an angle of 60° to horizontal ground. The ball
then strikes a vertical wall at the instant when the path of the ball becomes horizontal, as
shown in Fig. 2.2.
(i) By considering the vertical motion of the ball, calculate the time it takes to reach the wall.
[2]
(ii) Explain why the horizontal component of the velocity of the ball remains constant as it
moves to the wall.
[1]
(iii) Show that the ball strikes the wall with a horizontal velocity of 7.5ms-¹
[2]
(c) The mass of the ball in (b) is 0.40kg. It is in contact with the wall for a time of 0.12s and
rebounds horizontally with a speed of 4.3ms-¹.
(i) Use the information from (b)(iii) to calculate the change in momentum of the ball due to
the collision.
[2]
(ii) Calculate the magnitude of the average force exerted on the ball by the wall.
[1]