1. The figure shows a 100-kg block being released from rest from a height of 1.0 m. It then takes 0.53 s for it to reach the floor. What is the mass m of the block on the left? There is no friction or mass in the pulley, and the connecting rope is very light.

Question

A) 16 kg B) 14 kg C) 13 kg D) 11 kg

2. As shown in the figure, a 10-kg block on a perfectly smooth horizontal table is connected by a horizontal string to a 63-kg block that is hanging over the edge of the table. What is the magnitude of the acceleration of the 10-kg block when the other block is gently released?

A) 8.5 m/s2 B) 8.1 m/s2 C) 7.5 m/s2 D) 9.0 m/s2

3. A 958-N rocket is coming in for a vertical landing. It starts with a downward speed of 25 m/s and must reduce its speed to 0 m/s in 8.0 s for the final landing.
(a) During this landing maneuver, what must be the thrust due to the rocket's engines?
(b) What must be the direction of the engine thrust force?

4. A 200-N sled of slides down a frictionless hillside that rises at 37° above the horizontal. What is the magnitude of the force that the hill exerts on the sled parallel to the surface of the hill?
A) 200 N B) 120 N C) 160 N D) 150 N E) 0 N

5. The coefficients of static and kinetic friction between a 3.0-kg box and a horizontal desktop are 0.40 and 0.30, respectively. What is the force of friction on the box when a 15-N horizontal push is applied to the box?
A) 12 N B) 8.8 N C) 15 N D) 6.0 N E) 4.5 N
6. A 10-kg sign is held by two ropes as shown in the figure. What is the tension on rope A?

A) 44 N B) 69 N C) 72 N D) 88 N E) 98 N

7. A 50-kg box is being pushed along a horizontal surface. The coefficient of static friction between the box and the ground is 0.65, and the coefficient of kinetic friction is 0.35. What horizontal force must be exerted on the box for it to accelerate at 1.2 m/s2?
A) 60 N B) 120 N C) 170 N D) 230 N E) 490 N

8. As shown in the figure, block B on a horizontal tabletop is attached by very light horizontal strings to two hanging blocks, A and C. The pulleys are ideal, and the coefficient of kinetic friction between block B and the tabletop is 0.100. The masses of the three blocks are mA = 12.0 kg, mB = 7.00 kg, and mC = 10.0 kg. Find the magnitude and direction of the acceleration of block B after the system is gently released and has begun to move.


9. The figure shows a block of mass m resting on a 20° slope. The block has coefficients of friction and with the surface of the slope. It is connected using a very light string over an ideal pulley to a hanging block of mass 2.0 kg. The string above the slope pulls parallel to the surface. What is the minimum mass m so the system will remain at rest when it is released from rest?


A) 2.1 kg B) 3.3 kg C) 1.3 kg D) 3.6 kg

Answer 1

Check my answers?
1.C, 2.B, 3.?, 4.E, 5.D, 6.A(angle A=45, B=30, 7.D, 8. To the left,? (block A is hanging off the left side, block C is on the right), 9.?

Answer 2

3. V = Vo + a*t = 0.
25 + a*8 = 0, a = -3.1025 m/s^2

Thrust = M*a = 958/9.8 * (-3.125) = -305.5 N.

5. M*g = 3.0 * 9.8 = 29.4 N. = Wt. of block = Normal(Fn).
Fs = u*Fn = 0.4 * 29.4 = 11.8 N.

7. M*g = 50 * 9.8 = 490 N. = Wt. of box = Normal(Fn).
Fk = u*Fn = 0.35*490 = 171.5 N.

F - Fk = M*a.
F = Fk + M*a = 171.5 + 50*1.2 = 231.5 N.