Physics Homework Question?

Question

A projectile is fired at an upward angle of 40.0 ∘ from the top of a 160 m cliff with a speed of 155 m/s .

What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)

Answer 1

Step 1:

The object is fired at an upward angle of .

The height of the cliff is .

The speed of object is .

Find the maximum height reached by the object with respect to cliff.

The vertical component of velocity is .

Substitute and .

.

Maximum height .

Substitute and .

.

The maximum height reached by the object with respect to cliff .

The total height of the object with respect to ground is .

.

Step 2:

Find the speed of the projectile when it reaches the ground .

Using law of conservation of energy, Potential energy transferred is equal to the kinetic energy gained.

The total energy of object at maximum height is equal to the total energy at ground.

.

At maximum height, the kinetic energy of the object is zero.

At the ground, the potential energy of the object is zero.

Therefore, .

.

The speed of the projectile when it reaches the ground is .

Solution:

The speed of the projectile when it reaches the ground is .