9702_s22_qp_11 Question 6

A ball is thrown horizontally with a speed of 10.0 m s^–1 above horizontal ground. The ball hits the ground after a time of 3.0 s. 

Air resistance is negligible. 

What is the speed of the ball just before it hits the ground? 

A 10 m s^–1 

B 29 m s^–1 

C 31 m s^–1 

D 39 m s^–1  

ANSWER: C

The Physics Behind 

• The speed is the magnitude of the velocity of ball just before it hits the ground.
• This can be calculated using the Pythagorean Theorem

v² = v_x² + v_y²

where v_x is the horizontal speed and v_y is the vertical speed 

• The vertical speed v_y can be calculated using the equation of motion [from definition of acceleration],

v_y = u + at

where u is initial vertical speed [zero] and t is 3.0 s.