physics questions?

Question

1. If a nonezero net force is acting on an object, than the objects is defintely

A. At rest C. Being Accelerated

B. Moving with a constant veloctiy D. Losing Mass

2. A sailboat with a mass of 2.0 * 10^3 kg experiences a tidal force of 3.0 * 10^3N directed to the east and a wind force against its sails with a magnitude of 6.0 *10^3N directed toward the northewest (45 degrees N of W). What is the magnitude of the resultant acceleration of the boat? (My answer was 4.7 m/s^2)

3. A crate is carried in a pick up truck traveling horizontally at 15.0 m/s. The truck applies the brakes for a distance of 28.7m while stopping with uniform adcceleration what is the coefficient of static frictiion between the crate and the truck bed if the crate does not slide?

A. .400 C. .892
B. .365 D. .656

4. what is the magnitude + direction of the net external force on the rope 75 n to the left and 102 n to the right.
thanks in advance.

Answer 1

Well,

1 C. from F=ma, since F is non zero, then a has to be non zero.

2. vector addition. work it out.

3. A 0.4

Work out the decelerration. This force acts on the crate,
since the crate does not slip, its balanced by the
uN force of kinetic friction.

so uN = ma, u = ma/N = ma/mg = a/g.
a is the decceleration
distance travelled d = vt + 1/2at^2,
and t = v/a
where v = 15 and d = 28.7, so two equations in two unknows.

4. vector addition 27n to the right

Answer 2

hmm..this is too much work to get 10 pts if I get the best answer. but for 2 point, I'll write this.