Task R1 Problems

1. A 63.0-kg sprinter starts a race with an acceleration of 4.20 m/s2. What is the net external force on him?

3. A cleaner pushes a 4.50-kg laundry cart in such a way that the net external force on it is 60.0 N. Calculate the magnitude of its acceleration.

7. (a) If a rocket sled with 4 burners starts with only one rocket burning, what is the magnitude of its acceleration? Assume that the mass of the system is 2100 kg, the thrust T is 2.4 × 104 N, and the force of friction opposing the motion is known to be 650 N.
(b) Why is the acceleration not one-fourth of what it is with all rockets burning?

9. Suppose two children push horizontally, but in exactly opposite directions, on a third child in a wagon. The first child exerts a force of 75.0 N, the second a force of 90.0 N, friction is 12.0 N, and the mass of the third child plus wagon is 23.0 kg.
(a) What is the system of interest if the acceleration of the child in the wagon is to be calculated?
(b) Draw a free-body diagram, including all forces acting on the system.
(c) Calculate the acceleration.
(d) What would the acceleration be if friction were 15.0 N?

11. A rocket sled accelerates at a rate of 49.0 m/s2. Its passenger has a mass of 75.0 kg.
(a) Calculate the horizontal component of the force the seat exerts against his body. Compare this with his weight by using a ratio.
(b) Calculate the direction and magnitude of the total force the seat exerts against his body.

13. The weight of an astronaut plus his space suit on the Moon is only 250 N. 

a) How much do they weigh on Earth? 

b) What is their mass on the Moon? 

c) On Earth?