2015 Physics WAEC (WASSCE) Essay Past Questions (Paper 2)

Question 1

(a) What is a projectile?

Answer

Any object thrown into the air and allowed to fall freely under the influence of gravity is called a projectile.

The trajectory, or curved motion, or the path taken or described by a projectile while in the air is a trajectory.

A projectile motion is a curved motion described by a falling object in the air.

(b) Give the reason why the horizontal component of the velocity of a projectile remains the same at every point of its flight.

Answer

There is only one force acting on the object in the air, that is due to gravity, acting downwards. Since no force is acting in a horizontal direction therefore the magnitude of velocity and angle remain constant.

Mathematically,

v_x ² = u_x ² + 2gs

g = 0

∴ v_x ² = u_x ² + 0

v_x ² = u_x ²

∴ v_x  = u_x

Question 2

A body is projected at an angle of 30^o to the horizontal with a velocity of 150 ms^-1 . Calculate the time it takes the greatest height. [Take g = 10 ms^-2 and neglect air resistance]

Answer

Given:

• θ = 30^o
• u = 150 ms^-1
• t = ?
• g = 10 ms^-2
• The time taken to reach maximum height, t =?

Recall that

t = \(\frac{usin \theta}{g}\)

t = \(\frac{150 \: \times \: sin 30^o}{10}\)

t = \(\frac{75}{10}\)

= 7.5 s