Home Assignment:
CLASS 11: Physics Motion in a Plane Worksheet 65
ENGLISH A projectile shot at an angle of 60° above the horizontal ground strikes a vertical wall 30 m away
1 at a point 15 m above the ground. Find the speed with which the projectile was launched and the
speed with which it strikes the wall.
2 A cricket ball is thrown at a speed of 28 m/s in a direction 30° above the horizontal. Calculate:
(a) the maximum height.
(b) the time taken by the ball to return to the same level.
(c) the horizontal distance from the point of projection to the point where the ball returns to the
same level.
3 A man whirls a stone round his head on the end of a string 4 m long. Can the string be in a
horizontal plane ?
If the stone has a mass of 0.4 kg, and the string will break if the tension in it exceed 8 N, what is
the smallest angle the string can make with the horizontal ? What is the speed of the stone ? (take
g = 10 ms−2)
4 A ball is thrown vertically upwards with a velocity of 20 m/s from the top of a building of height 25
m from the
ground
(a) How high will the ball reach ?
(b) How long will it take for the ball to reach the ground ?
(c) Trace the trajectory of motion of this ball.
5 A particle has a displacement of 12 m towards east and 5 m towards north and 6 m vertically
upwards. Find the magnitude of the sum of these displacements.
6 A string can withstand a tension of 25 N. What is the greatest speed at which a body of mass 1 kg
can be whirled in a horizontal circle using a 1 m length of the string ?
7 A bullet fired at an angle of 30° with the horizontal hits the ground 3 km away. By adjusting its
angle of projection, can one hope to hit a target 5 km away ? Assume the muzzle speed to be
fixed, and neglect air resistance. (Take g = 10 ms−2)
8 From the top of a building 19.6 m high, a ball is projected horizontally. After how long does it strike
the ground ? If the line joining the point of projection to the point where it hits the ground makes
an angle of 45° with the horizontal, what is the initial velocity of the ball ?
9 A fighter plane flying horizontally at an altitude of 1.5 km with speed 720 km/hr passes directly
overhead an anti-aircraft gun. At what angle from the vertical should the gun be fired for the shell
with muzzle speed 600 ms−1 to hit the plane ?
At what minimum altitude should the pilot fly the plane to avoid being hit ?
(Take g = 10 ms−2)
10 The ceiling of a long hall is 25 m high. What is the maximum horizontal distance that a ball thrown
with a speed of 40 ms−1 can go without hitting the ceiling of the hall ?
11 A shell bursts on contact with the ground and the fragments fly in all directions with speeds upto
39.2 m/s. Show that a man 78.4 m away is in danger for seconds.
12 A cricket ball is thrown at a speed of 28 m/s in a direction 30° above the horizontal. Calculate : (a)
the maximum height (b) the time taken by the ball to return to the same level (c) the horizontal
distance from the thrower to the point where the ball returns to the same level.
