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All questions of Projectile Motion for JAMB Exam

 In case of a projectile motion, what is the angle between the velocity and acceleration at the highest point?
  • a)
  • b)
    45°
  • c)
    90°
  • d)
    180°
Correct answer is option 'C'. Can you explain this answer?

Suresh Iyer answered
At the highest point, velocity is acting horizontally and acceleration ( = acceleration due to gravity) is acting vertically downwards. Therefore, at the highest point the angle between velocity and acceleration is 90 .

A cricketer can throw a ball to a maximum horizontal distance of 100m. With the same speed how much high above the ground can the cricketer throw the same ball?
  • a)
    50 m
  • b)
    100 m
  • c)
    150 m
  • d)
    200 m
Correct answer is option 'A'. Can you explain this answer?

Meera Singh answered
Let u be the velocity of projection of the ball. The ball will cover maximum horizontal distance when angle of projection with horizontal, θ = 45. Then Rmax = u2/g = 100m
If ball is projected vertically upwards (θ = 90) from ground then H attains maximum value.

∴  The height to which cricketer can through the ball is = Rmax/2 = 100/2 = 50m.

Two projectiles are are fired from the same point with the same speed at angles 60° and 30° respectively. Which one of the follwing is true?
  • a)
    Their horizontal ranges will be the same
  • b)
    Their maximum heights will be the same
  • c)
    Their landing velocities will be the same
  • d)
    Their times of flight will be the same
Correct answer is option 'A'. Can you explain this answer?

Uday Dasgupta answered
Horizontal Range
- The horizontal range of a projectile is the distance traveled horizontally before hitting the ground.
- The horizontal range of a projectile is given by the formula R = (v^2 * sin(2θ))/g, where v is the initial velocity, θ is the angle of projection, and g is the acceleration due to gravity.
- When both projectiles are fired from the same point with the same speed, the initial velocity v is the same for both.
- Since sin(2*60°) = sin(120°) = sin(2*30°), the horizontal ranges of the projectiles fired at 60° and 30° will be the same.
Therefore, the correct option is:

a) Their horizontal ranges will be the same

 The equations of motion of a projectile are given by x = 36t m and 2y = 96t - 9.8t2 m. The angle of projection is
  • a)
    sin−1(4/5)
  • b)
    sin−1(3/5)
  • c)
    sin−1(4/3)
  • d)
    sin−1(3/4)
Correct answer is option 'A'. Can you explain this answer?

Vivek Patel answered
Given x = 36t
and 2y = 96t − 9.8t2
or y = 48t − 4.9t2
Let the initial velocity of projectile be u and angle of projection θ. Then, Initial horizontal component of velocity,

A ball is thrown from the top of a tower with an initial velocity of 10 m s-1 at an angle ot 30° with the horizontal. If it hits the ground at a distance of 17.3 m from the base of the tower, the height of the tower is (Take g = 10 m s-2)
  • a)
    5 m
  • b)
    20 m
  • c)
    15 m
  • d)
    10 m
Correct answer is option 'D'. Can you explain this answer?

Riya Banerjee answered
The ball is thrown at an angle, θ = 30o.
Initial velocity of the ball, u = 10 m/s 
Horizontal range of the ball, R = 17.3 m
We know that, R = u cosθ t,
 where t is the time of flight 

using equation of motion we get:-

⟹ Height of tower, h = 10 m

If R and H represent horizontal range and maximum height of the projectile, then the angle of projection with the horizontal is:
  • a)
    tan−1 (H/R)
  • b)
    tan−1 (2H/R)
  • c)
    tan−1 (4H/R)
  • d)
    tan−1 (4R/H)
Correct answer is option 'C'. Can you explain this answer?

Nandini Sharma answered
Understanding Projectile Motion
In projectile motion, the angle of projection determines the trajectory of the projectile. When we denote the horizontal range as \( R \) and the maximum height as \( H \), we can derive the angle of projection.

Key Formulas
- The horizontal range \( R \) of a projectile is given by:
\[
R = \frac{v^2 \sin(2\theta)}{g}
\]
- The maximum height \( H \) attained by a projectile is given by:
\[
H = \frac{v^2 \sin^2(\theta)}{2g}
\]
Where:
- \( v \) = initial velocity
- \( g \) = acceleration due to gravity
- \( \theta \) = angle of projection

Relationship Between H and R
To find the angle \( \theta \), we can manipulate these equations.
1. From the maximum height formula:
\[
v^2 = 2gH \cdot \frac{1}{\sin^2(\theta)}
\]
2. Substituting \( v^2 \) in the range formula:
\[
R = \frac{(2gH / \sin^2(\theta)) \cdot \sin(2\theta)}{g}
\]
3. Simplifying gives:
\[
R = \frac{2H \sin(2\theta)}{\sin^2(\theta)}
\]
Using the identity \( \sin(2\theta) = 2\sin(\theta)\cos(\theta) \):
\[
R = \frac{4H \cos(\theta)}{\sin(\theta)}
\]
4. Rearranging leads to:
\[
\tan(\theta) = \frac{4H}{R}
\]

Final Expression for Angle of Projection
Thus, the angle of projection \( \theta \) can be found using:
\[
\theta = \tan^{-1}\left(\frac{4H}{R}\right)
\]
Hence, the correct choice is option **C**: \( \tan^{-1}\left(\frac{4H}{R}\right) \).

Rain is falling vertically with a speed of 30 ms−1. A woman rides a bicycle with a speed of 12 ms−1 in east to west direction. In which direction she should hold her umbrella?
  • a)
    At an angle of tan−1(2/5) with the vertical towards the east.
  • b)
    At angle of tan−1(2/5) with the vertical towards the west.
  • c)
    At angle of tan−1 (5/2) with the vertical towards the east.
  • d)
    At angle of tan−1 (5/2) with the vertical towards the west.
Correct answer is option 'B'. Can you explain this answer?

Suresh Iyer answered
In the figure,  represents the velocity of rain and vb​ the velocity of the bicycle, the woman is riding. To protect herself from rain, the woman should hold her umbrella in the direction of the relative velocity of rain with respect to the bicycleFrom figure,

Therefore, the woman should hold her umbrella at an angle of tan−1(2/5​)with the vertical towards the west.

The speed with which the stone hits the ground is
  • a)
    15 m s-1
  • b)
    90 m s-1
  • c)
    99 m s-1
  • d)
    49 m s-1
Correct answer is option 'C'. Can you explain this answer?

Riya Banerjee answered
Motion along horizontal direction, ↓+ ve
ux = 15ms−1, ax = 0 
vx = ux + axt = 15 + 0 × 10 = 15ms−1
Motion along vertical direction,
uy = 0,ay = g
vy = uy + ayt = 0 + 9.8 × 10 = 98ms−1
∴ Speed of the stone when it hits the ground is

Then the distance from the thrower to the point where the ball returns to the same level is
  • a)
    58 m
  • b)
    68 m
  • c)
    78 m
  • d)
    88 m
Correct answer is option 'C'. Can you explain this answer?

Anjali Sharma answered
Given data,
u = 30ms−1
θ = 300
g = 10ms−2
The distance from the thrower to the point where the ball returns to the same level is

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