Will someone please help me with these Physics questions.

Question

A pebble that is 3.81 m from the eye of a tornado has a tangential speed of 124 m/s. What is the magnitude of the pebble's centripetal acceleration? Remember the centripetal acceleration equation is  a=v² / r.

a. 32 m/s²

b. 435 m/s²

c. 85 m/s²

d. 4036 m/s²

Find the magnitude of the gravitational force exerted on a 66.5 kg astronaut on the surface of Planet X if the planet has a radius of 4.40 x 10⁶ m and a mass of 8.43 x 10²³ kg.(Use G= 6.67 x 10⁻¹¹ Nm/kg²) 

a. 246 N

b. 193 N

c. 38.5 N

d. 651 N

A ball attached to a string is whirled in a circle. If the string breaks, what causes the ball to move in a straight line?

a. inertia

b. centripetal force

c. centripetal acceleration

d. centrifugal force

A boy can raise a rock that weighs 120 N by using a lever and applying a force of 25 N. What is the mechanical advantage of the lever?

a. 4.8

b. 225

c. .21

d. 3.5

A dog sits 1.25 m from the center of a merry go round and revolves at a tangential speed of 2.0 m/s. If the dog's mass is 19.3 kg, what is the magnitude of the centripetal force on the dog?

a. 40. N

b. 61.8 N

c. 103 N

d. 21.3 N

Answer 1

For the first problem I’m going to make an assumption that the 3.81 m represents the radius or the distance from the center of the tornado because the problem indicates that it is 3.81 m from the eye (center) of the tornado. So I just applied the equation of acceleration = 124 ²/3.81. The answer is 4036 m/s squared, which is letter D of the multiple-choice

The second problem is a direct application of the field strength between two bodies given the mass of each body, the gravitational constant, and the distance between the two bodies. The equation is F = (G M₁ and M₂)/D². This comes out to be 193 N which is B of the multiple-choice.