A rock is thrown from the upper edge of a tall cliff at some angle above the horizontal. It reaches its highest point and starts falling down. Which of the following statements about the rock's motion are true just before it hits the ground?

a. Its speed is the same as it was just as it was launched

b. Its horizontal velocity component is the same as it was just as it was launched

c. Its velocity is vertical.

d. Its vertical velocity component is the same as it was just as it was launched.

e. Its horizontal velocity component is zero.

b. Its horizontal velocity component is the same as it was just as it was launched

Explanation:

When the rock is thrown from the upper edge of the cliff, at some angle with the horizontal. There is no any acceleration in horizontal direction, therefore, the horizontal velocity remains the same, whereas there is a constant downward acceleration of the magnitude g= 9.81 m/s^2. This causes the increase in vertical velocity of the rock in downward direction.

therefore  true statement just before it hits the ground

b. Its horizontal velocity component is the same as it was just as it was launched.

heat the gas and measure the pressure